Added callback support for modal directive. Fixed UI for login modal
* Callback allows the controller to execute any code on the close event
  of the modal dialog. Such as clearing fields.
* Fixed Login modal so fields will clear on cancel or dismiss of modal
* Fixed Login modal so remember me checkbox doesnt flicker on login
* Fixed Login modal so username field will autofocus on open. This was
  solved by adding ng-if to the username field so auto focus when the
  field becomes visible.