[RESEARCH ONLY] Hook up DOM diffing to live development

* Replaced the old DOMHelpers-based code in HTMLInstrumentation with the SimpleDOMBuilder. I was able to get most of the unit tests in HTMLInstrumentation for well-formed HTML to pass after this change (and the actual highlighting functionality seemed to mostly work), but there were issues with HTML that had implicit end tags, etc.
* Merged in Jason's remote-object-editing branch.
* Hooked up change events to call the DOM differ and update when attributes are added/changed/removed.