Clear ActiveMailer deliveries after all specs

ActiveMailer is set to clear the deliveries array after Mailer specs run,
but not after request or controller specs. This causes the array to be
prepopulated when specs run after a request or controller array that
creates mail. This fixes that.

Also switches to using lets in the attendance mailer spec for increased
clarity
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
Merge pull request #191 from TeaWithStrangers/intermittent-mailer-fix

Clear ActiveMailer deliveries after all specs
Spec for GetOrCreateUser
Integration test for existing user being redirected
Add integration test for existing user logic
Update tea time factories and corresponding tests
Add CancelTeaTime Service Object, use it
Upgrade gems to latest revisions, fix Rails security vulnerability
Speed up specs some by switching to before(:all) blocks
Merge pull request #190 from TeaWithStrangers/service-object-logic-consolidation

Add Service Object to Consolidate User Creation Logic
Merge pull request #192 from TeaWithStrangers/send-cancellation-on-destroy

Send Tea Time Cancellation on destroy
remove incomplete test from TT mailer
fix merge
flash message styles