Change backend to be aligned with API

 - Allow the possibility to get unscoped tokens
 - Move user_id to UUID on voms backend
 - Added tests against the token backend
 - Updated documentation

Change-Id: If1deb76c9f8a58170a8965f2334642e8d19b7179
Added setup.py file and updated documentation.
Change tenant to project in exceptions and identity API calls.