restore add to selection button

explorerjs.html

@@ -286,13 +286,13 @@
             <li id="crowdsourcing_answer" class="nav crowdsourcingModule navbar-lower"></li>
 
             <!-- checkbox -->
-            <!-- <li class="navbar-lower">
+            <li class="navbar-lower">
               <input id="checkboxdiv" onclick="alertCheckBox(this);"
                     title="Add next search results to current selection"
                     class="nav btn btn-info"
                     type="checkbox">
               <span style="position: relative; top: 4px;">Add to selection</span>
-            </li>  -->
+            </li>
 
           </ul>