Better Management of Node eventHandlers add/remove

[jhickman]

Currently, the ShortcutTrapper instance will add event handlers to the provided node in the constructor and never remove. It would be nice to coordinate the add/remove with the number of bindings. This way, if the ShortcutTrapper gets cleared, it should remove the handlers and not 'technically' be tied to that node anymore.

[jhickman]

Thinking through this, the instance isn't holding a copy of the Node, and in order to add/remove the handlers based upon the size() of the bindings collection, then we would have to hold onto it.