[Toolbar] Implement a public API for adding toolbars (#1908)

* [API] Implement a toolbar registry and a plugin to allow providing a toolbar for a selected object.
* Modify the mct-toolbar directive to get the toolbar structure from a provider based on selection.
* Implements the layout toolbar in the layout bundle

platform/features/layout/res/templates/fixed.html

@@ -41,7 +41,7 @@
         <mct-include key="element.template"
                      parameters="{ gridSize: controller.getGridSize() }"
                      ng-model="element">
-        </mct-include>       
+        </mct-include>
     </div>
     <!-- Selection highlight, handles -->
     <span class="s-selected s-moveable" ng-if="controller.isElementSelected()">

platform/features/layout/res/templates/layout.html

@@ -41,7 +41,7 @@
          ng-class="{ 'no-frame': !controller.hasFrame(childObject), 's-drilled-in': controller.isDrilledIn(childObject) }"
          ng-repeat="childObject in composition"
          ng-init="controller.selectIfNew(childObject.getId() + '-' + $id, childObject)"
-         mct-selectable="controller.getContext(childObject, true)"
+         mct-selectable="controller.getContext(childObject)"
          ng-dblclick="controller.drill($event, childObject)"
          ng-style="controller.getFrameStyle(childObject.getId())">