Convert API controller specs into rspec 3 syntax
Refactors content and element permissions.

Uses newly introduced scopes and delegate methods on content model.
Make ApplicationController patch reloadable

and don't cache classes in tests!
Adds new API endpoints for contents

Adds three new API endpoints for loading Alchemy::Contents via json:

* /api/contents.json
* /api/elements/:element_id/contents.json
* /api/elements/:element_id/contents/:name.json
Convert essence_picture serializer spec into rspec 3 syntax