add epoch 3 to tiles dropdown

src/app/tiles/tiles.component.html

@@ -23,6 +23,9 @@
           <li ngbDropdownItem>
             <button type="button" class="btn btn-link w-100 p-0 text-left" (click)="setEpoch(2)">Epoch 2</button>
           </li>
+          <li ngbDropdownItem>
+            <button type="button" class="btn btn-link w-100 p-0 text-left" (click)="setEpoch(3)">Epoch 3</button>
+          </li>
         </ul>
       </div>
       <form (ngSubmit)="getMinitilesForEpoch()" class="form-inline col-auto pl-4" [formGroup]="formGroup">