* Add RegistrationSession object
* Add RegistrationSessionManager protocol
* Add skeleton RegistrationSessionManagerImpl - just kvstore persistence implemented
* Issue requests in RegistrationSessionManagerImpl
* let tests access the in memory kv store
* Add TSRequestOWSURLSessionMock. Rename OWSURLSessionMock
* Add DateProvider
* Take a dateProvider in RegistrationSessionManagerImpl
* Add tests for RegistrationSessionManager
* pre-emptively update timeout for tests. will remove once promise Scheduler code is merged
* PR comments
* Use Schedulers
