fix(uiSelectNoChoice): support bootstrap-multiple

While using ui-select-no-choice directive it doesn't apply for multiselect 
mode (bootstrap theme). Appropriate markup was missed for multiselect 
mode in template for bootstrap theme.

Closes #1614 & #1615

src/bootstrap/select-multiple.tpl.html

@@ -17,4 +17,5 @@
            ondrop="return false;">
   </div>
   <div class="ui-select-choices"></div>
+  <div class="ui-select-no-choice"></div>
 </div>