Swappable returns a boolean for saying if the swap occured or not

[mr]

I'm not sure if this is actually useful for anyone, but in my app it was useful to be able to have a drag and drop interface where some elements could not be dragged below a certain point. I changed Swappable to return a boolean which says if the swap actually happened. If it doesn't, it prevents the animation from playing. This prevents the animations from freaking out when you drag over something that you can't drag to.