changed text in sign up form header and change text in submit button
added sessions controller
added sessions resources to routes and email downcase callback method
set up controller actions in sessions controller
added email validation for user model and find_by_email_or_username method
added sessions form (new.html.erb)
added "notice:" to the success user create redirect method
added login path
add callback method to generate an auth_token for user
added current_user and authorize application controller methods
added flash messages and styling
changed color of flash alert/notice text