@starsirius => Render model references from API + more docs.

The meat of this PR is in the pages_controller which can now:

* Render JSON resources as examples from the API with things like `#{resource://artist/id=4d8b92b34eb68a1b2c0003f4}`.
* Render model field documentation directly from the machine description of the API with things like `#{modelref://Artist}`.

Do we still need the `artwork_id` here if we already have the `id` of the edition set? Or it can just return the artwork it belongs to without the param?