Add metadata viewing and editing commands

[thomas-senechal]

ATM, the only way to view metadata of a website is using the uploader website, which only shows some metadatas (like the title, description and keywords). Having a way to do that from the CLI could be useful to debug and to some projects.

Editing metadata is only possible using the upload command. Having a simpler and more direct way to view and edit metadata would be nice.

We should add a command to view the full metadata of a website, and a command to edit the metadata.

Most functions are already implemented, we mainly have to add the commands to the CLI.