Provide a mechanism to view the type at the end of :ref relations

[mgrbyte]

Currently, when viewing the generated schema of the database,
it's not possible to statically inspect the types assigned to a corresponding :ref.

pseudoace stored the information of what kind of information/object should "live" at the end of :ref
in the :pace schema.

The attributes to consider using are:

• :pace/obj-ref
• :pace.xref/obj-ref

As a first pass, attempt to add annotations to the current datomic-schema output, inline with every :ref occurrence.

[mgrbyte]

@khowe Found this In relation to the issue I raised in our last meeting regarding components representing different has-models on each end each vertex between related nodes.

[mgrbyte]

Superseded by #65