Update user roles in store after owner transfer

Closes #3466
- Transferring the owner role is now done via a separate
  endpoint and not through Ember-Data.  As a result the
  user role data needs to be updated manually.
- Updated the owner endpoint to return a response body
  containing the updated user objects.
- Updated tests.
Merge pull request #3480 from jaswilli/issue-3466

Update user roles in store after owner transfer