Change QAbstractItemView::startDrag() to a QEvent

It would be nice if QAbstractItemView::startDrag() would not be a function but two QEvent's. Something like QDragStartEvent and QDragStopEvent which is being sent to the widget which starts dragging. So the QApplication and all eventFilter()'s of the drag source would be notified that dragging begins. The behavior of QAbstractItemView::startDrag() could be changed without the need to derive from QTreeView and QListView only to override it.