Testing / Refactor

Please See Readme 
Summary:

-  Added unit and integration testing for 
    -  validations on all models - responses, questions and users
    -  configured Capybara login stub (see spec/support folder) 
    -  added FactoryGirl: defined factories and included for some tests
-  created current_user and redirect_to_signup helper methods 
-  switched from SQLite to PostgreSQL for database cleaner and integration testing