Added refresh to the bindingHandler

Added refresh to the bindingHandler to support clearing/modifying of the
bound observable.

js/bootstrap-multiselect.js

@@ -21,6 +21,9 @@
                 else if (allBindingsAccessor().options && allBindingsAccessor().options().length !== ms.originalOptions.length) {
                     ms.updateOriginalOptions();
                     $(element).multiselect('rebuild');
+                }
+				else {
+                    ms.refresh();
                 }
             }
         };