added no results found message when result array size == 0

src/main/webapp/app/mock-search/mock-search.component.html

@@ -16,6 +16,9 @@
                                (exerciseSelectionEvent)="selectExercise($event)">
             </jhi-exercise-card>
         </div>
+        <div *ngIf="results.length === 0" >
+            No results found
+        </div>
     </div>
 </div>