Added Edit_OnClick(), fixed issues MAGN4505

Issue:http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4505
@Benglin Please review it. Thanks
Can you please ensure that casting is successful and we are not calling methods over null object.
var menuItem = (MenuItem)sender;
if(null == menuItem)
   return;
var searchElement = (CustomNodeSearchElement)menuItem.DataContext;
if(null == searchElement)
   return;
var pathOfCustomNode = searchElement.Path;