method caching for current_user
UsersController, SessionsContoller are refactored.
Controllers are broken apart ProvidersController, ActivationsController.
'and' rather than &&
add index to account_activations provider, uid
user activator as a service
refactored about session
added provider_token model, migration
refactored with provider_token model.
Merge pull request #226 from DonutWorks/refactor/issue-174

Refactor/issue 174