Add a trigger to re-do enabledragndrop

We were trying to understand why when we added new elements, this trigger was not being called. There was no way built in to call it so I added an event for it. I think it would be really useful for a lot of people who are adding new elements to their shapeshift projects!

If you'd rather re-render the Coffee with the version of the compiler you're using, I totally understand that! Just thought this was a useful contribution in the short term to solve some issues that doesn't break anything.