quick fixes for mongoid to work

Please note that
1) generators are not changed, need to edit models manually
2) tests are not updated
hard-coded User and namespaced model

https://github.com/lynndylanhurley/devise_token_auth/issues/68
https://github.com/lynndylanhurley/devise_token_auth/issues/69
No need to use Time.parse
no active_record loading