Removed devise

Removed devise due to issues with overriding methods from Devise::Models::Authenticatable:
- serialize_from_session(id),
- serialize_into_session(resource).

Similar issues:
- http://stackoverflow.com/questions/14882871/i-need-simple-but-complete-instructions-for-implementing-a-devise-authentication
- https://github.com/plataformatec/devise/issues/2437