Added Devise and User

Followed RailsGirls Guide to Devise guides.railsgirls.com/devise/
Added Devise to Gemfile and performed Bundle Install to recreate Gemfile.lock
Added Header partial
Added to Header partial options including Login, Logout, Sign Up, and Edit Profile
Added to Header partial an section for Alerts Notices and Errors to be displayed
Added before_action to ApplicationController requiring users to login before accessing any pages
Get rid of devise that was already there
Merge pull request #3 from albertodotcom/dev_luke

Added Devise and User