Moved Login into Modal. Created generic modal directive
* Login is now moved into a modal window
* Modal directive uses a modal tag <modal></modal>
* Modals can be defined as:
<modal class="tiny" show="HeaderCtrl.show">
  <strong>Hello World</strong>
</modal>
* Controller must implement a close and open:
    this.show = false;
    this.openLoginModal = function() {
      ctrl.show = true;
    };

    this.closeLoginModal = function() {
      ctrl.show = false;
    };