Add GetOrCreateUser Service Object

* Configures application to load service objects everywhere
* Implements it in registrations_controller
* Attendance.rb change is due to wonky stash merge
Use GetOrCreateUser Service in TT Controller
Spec for GetOrCreateUser
Integration test for existing user being redirected
Add integration test for existing user logic
Merge pull request #190 from TeaWithStrangers/service-object-logic-consolidation

Add Service Object to Consolidate User Creation Logic