Authentication Module:

  * Added User model & migration.
  * Added User controller only index (only for setup purpose, it could be disappear on the future).
  * Added Devise views.
  * Added default host and port for mailer on development.
  * Added flash messages partial.
  * Added navigation partial with sign_in, sign_up, sign_out, profile links.
  * Configured devise user as confirmable. (account confirmation through email)