[Display Layout] Add delete button (#2251)

* Add delete button in the toolbar for removing items

* Mutate composition if there are no telemetry objects. Select the parent layout after deleting an item.

* Saving work

* Watch for index in the components and update it in the context.

* Select the parent after a composition is removed.

* Address reviewer's feedback.
- Rename mutatComposition() to removeFromComposition().
- Inline logic for filtering composition
- Use separate branches for each item type in trackItem().

* Address reviewer's requested changes

src/plugins/displayLayout/plugin.js

@@ -60,7 +60,8 @@ export default function () {
                     getSelectionContext() {
                         return {
                             item: domainObject,
-                            addElement: component && component.$refs.displayLayout.addElement
+                            addElement: component && component.$refs.displayLayout.addElement,
+                            removeItem: component && component.$refs.displayLayout.removeItem
                         }
                     },
                     destroy() {