[editor] Fix faulty drag and drop behaviour of canvas elements

The Material drag and drop stuff does not play well with the 
implementation of elements being styled dynamically via CSS. The extra 
div element pulls them apart avaoiding problems.

projects/editor/src/app/components/unit-view/page-view/canvas/canvas-drag-overlay.component.ts

@@ -11,9 +11,11 @@ import * as ComponentUtils from '../../../../../../../common/component-utils';
 @Component({
   selector: 'app-canvas-drag-overlay',
   template: `
-    <div cdkDrag [cdkDragData]="this.element" (click)="click($event)"
-         [ngStyle]="style">
-      <ng-template #elementContainer></ng-template>
+<!--    Needs extra div because styling can interfere with drag and drop-->
+    <div cdkDrag [cdkDragData]="this.element" (click)="click($event)">
+      <div [ngStyle]="style">
+        <ng-template #elementContainer></ng-template>
+      </div>
     </div>
     `,
   styles: [