Avoid memory leaks during refresh - DO NOT MERGE

This is intended to get some discussion around a solution for memory leaks around elements that are removed during a refresh (http://bugs.jqueryui.com/ticket/10056).

Unfortunately, I don't think there's a general solution we can apply. Every widget that handles a refresh will need to manually track the removed elements and pass them to `._off()`.
For 1.12/2.2 we could add a method to clear off the `.prevObject` and you could polyfill it? The hard part is gonna be coming up with a name. :smile_cat: