Modernize OAuthserver and provide more context on "no permission" exception
- Generally modernize some of this code.
- Add some more information to PolicyExceptions so the new RequestExceptionHandler can handle them properly.
Test Plan: Failed authorizations, then succeeded authorizations. See next diff.
Reviewed By: chad
Maniphest Tasks: T7173
Differential Revision: https://secure.phabricator.com/D14050