Update data model (#306)

* feat: make title of a file optional

* refactor: template -> templateId

Author: jkoenig134

_docs_integrate/data-model-overview.md

@@ -104,7 +104,7 @@ A Relationship between two Identities is the prerequisite for them to exchange M
 | Name             | Type                                                                                                                                             | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | Remarks                                       |
 | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------- |
 | id               | `string`                                                                                                                                         | {% include descr_id class="Relationship" prefix="REL" %}                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                               |
-| template         | [`RelationshipTemplate`](#relationshiptemplate)                                                                                                  | The RelationshipTemplate that was used to establish this Relationship.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |                                               |
+| templateId       | `string`                                                                                                                                         | The ID of the RelationshipTemplate that was used to establish this Relationship.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                               |
 | status           | `"Pending"` \| `"Active"` \| `"Rejected"` \| `"Revoked"` \| `"Terminated"` \| `"DeletionProposed"`                                               | The status of this Relationship. <br>{::nomarkdown}<ul><li>Pending: the Relationship was created, but not yet accepted by the recipient. In this state you cannot send Messages yet.</li><li>Active: this means that the Relationship is active. As long as it is active, both participants can exchange Messages.</li><li>Rejected: the Relationship was rejected by the recipient.</li><li>Revoked: the Relationship was revoked by the sender.</li><li>Terminated: No Messages can be sent. Either side can request reactivation from the peer.</li><li>Deletion Proposed: Your peer has decomposed the Relationship, i. e. locally deleted the Relationship and data transmitted during it.</li></ul>{:/} |                                               |
 | creationContent  | [`RelationshipCreationContent`](#relationshipcreationcontent) \| [`ArbitraryRelationshipCreationContent`](#arbitraryrelationshipcreationcontent) | The content sent along when the Relationship is initiated. If the `template` contains a [RelationshipTemplateContent](#relationshiptemplatecontent), `RelationshipCreationContent` has to be used. Otherwise, an `ArbitraryRelationshipCreationContent` is used, which can be filled with anything.                                                                                                                                                                                                                                                                                                                                                                                                           | will be encrypted before sent to the Backbone |
 | peer             | `string`                                                                                                                                         | The `address` of the [Identity](#identity) with which you have this Relationship.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |                                               |
@@ -186,7 +186,7 @@ The content of the File can be downloaded separately by executing the [Download
 | filename           | `string`                | The name of the file as it was on the device that uploaded it.                                                        | will be encrypted before sent to the Backbone |
 | filesize           | `number`                | The size of the plaintext file in bytes.                                                                              | will be encrypted before sent to the Backbone |
 | mimetype           | `string`                | The [mimetype](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types) of the file. | will be encrypted before sent to the Backbone |
-| title              | `string`                | A human readable title of the file, which can be defined when uploading the File.                                     | will be encrypted before sent to the Backbone |
+| title              | `string` \| `undefined` | A human readable title of the file, which can be defined when uploading the File.                                     | will be encrypted before sent to the Backbone |
 | description        | `string` \| `undefined` | A human readable description of the file, which can be defined when uploading the File.                               | will be encrypted before sent to the Backbone |
 | isOwn              | `boolean`               | {% include descr_isOwn class="File" %}                                                                                | saved only locally                            |
 | truncatedReference | `string`                | {% include descr_truncatedReference class="File" %}                                                                   | saved only locally                            |