Update some of the test dependencies
Switch to separate spec_helper and rails_helper.

This follows what RSpec3 generates when being setup on a new project.
Put all integration specs in the same place

Also name the files more clearly.
Add publishing_app field to integration tests.

So that we're covering all the fields mentioned in the docs.
Move upserting of content items into the model.

This removes a lot of this logic from the controller, which wasn't the
right place for it really.
Gracefully handle unexpected fields in the input.

Currently extra fields in the intput cause a 500 error.  This changes
this so that they now return a 422.