Feature/omniauthhelper rehash

- Fixed #20 by rewriting OmniAuthHashHelper and OmniAuthHelper into `lib/login/omni_auth_hash_manager/validator.rb` and `mapper.rb`
- Full coverage for this new strategy
- Rewrote old tests to work in new strategy
Client is user/app combination.

Authorization code is set after the client authorizes the application for this provider.

OAuth2 App is a registered application with this provider.