[Completes #57082294] Third-party applications can verify other application's credentials

 - Finish up specs to verify credentials API

 - API controller refactoring.

 - Remove extra api/profiles controller.

 - Update oauth2-provider gem to revision that support client_credentials grant type.

 - Refactor oauth_controller, modify for client_credentials grant types.
Remove status from Notifications API responses.
Remove MAX.gov as an authentication provider.