Mouse gets away from the object it is dragging

[samreid]

In balloons-and-static-electricity the drag handler is provided by SimpleDragHandler, and the pointer can get away from the object it is dragging (if you drag it against the wall for example). Scenery should provide support for a drag handler that stores the relative location of the object and uses it for dragging. I am also having this problem with the objects and sliders in Forces and Motion Basics. This is very closely related to #3

This could be handled in balloons but I think it would be superior and more maintainable to provide support directly in scenery. In my opinion, this behavior should be fixed before our July milestone.

[jonathanolson]

Recommend handling in new drag listener, see #131.

Sound acceptable?

[samreid]

We have good support for this in MovableDragHandler, I wouldn't mind if we also had good support for it in the next generation scenery input listeners and we can track it in #131.