[WIP] Add destructors to JS objects (required by AjaxManager plugin)

Work in progress. There is a issue with TV fields - they and their TreeDrops (created by MODx.makeDroppable) should be destroyed properly. Otherwise Drag'n'Drop is broken (ExtJS while dragging tries to access removed DOM nodes).
This fix somehow disappeared. It was merged as https://github.com/modxcms/revolution/commit/a0d3ae546babf1c656a7e8cdcdc0129cea8ea57f