started implementing registration process
reconfigured groupongs in gem file and added letter opener gem
added development configuration for letter_opener
completed tests for flash message and email sending
wrote out test definitions for invalid input context and implemented first test together with username presence validation on the model level
tests to validate uniqueness of username on controller and model level
implemented email validations on user model and respective tests on the user registration process
implemented tests for password_confirmation and first name presence
finished last tests for user registration
added flash messages on registration errors
Merge pull request #3 from sammy/register_feature

User registration implementation