Added an event trigger to stop the spinner

When you use the convenient Ladda.bind functionality, you lose any smart way to manipulate a single jQuery element, to stop a Ladda spinner.  Using this small hack, you can use:

$("#thebutton").trigger('ladda-stop');

It's helpful in cases where designers use Ladda.bind on a page with many buttons, yet an AJAX action should only stop one.  This eliminates the need to burden AJAX calls with a ton of Ladda-specific code.