Affix logic for widget area and update date format.

* Create directive for "widgetArea" and add affix logic that handles
  login transition.

* Update displayed date format.
Implement ajax signup.

* Added sign up logic to auth.js.

* Refactored welcome element collapse and tasks service population
  out of "viewCtrl" into method of $auth service.

* Add modal for sign up.

* Make ".help-block" styles top-level.

* Updated registrations controller to make json response and
  correctly handle parameters.

* Give login failures a 422 status code to be consistent with
  registration controller.