Restore and speed up sorted display of inner nav

Key points:<br>* Inner nav now has the ability to add new widgets individually, instead of having to take the whole sorted list each time<br>* The widgets_updated event is now fired from DashboardWidgets again, and specifically targets the individual adding of widgets<br>* Display of the inner nav is delayed until 50ms after it stops receiving update events, which makes it snappy but not visibly resorted.