Adding 'btnSubmit' ID to contact form submit button as expected by...

Adding 'btnSubmit' ID to contact form submit button as expected by contact_me.js. Fixes issue where user can click submit button repeatedly thinking nothing has happened causing multiple emails to be sent.

index.html

@@ -507,7 +507,7 @@
                                     </strong>
                                 </li>
                             </ul>
-                            <button type="button" class="btn btn-default" data-dismiss="modal"><i class="fa fa-times"></i> Close</button>
+                            <button id="btnSubmit" type="button" class="btn btn-default" data-dismiss="modal"><i class="fa fa-times"></i> Close</button>
                         </div>
                     </div>
                 </div>