Restore and speed up sorted display of inner nav

Key points:
* Inner nav now has the ability to add new widgets individually, instead of having to take the whole sorted list each time
* The widgets_updated event is now fired from DashboardWidgets again, and specifically targets the individual adding of widgets
* Display of the inner nav is delayed until 50ms after the view is rendered and it stops receiving update events, which makes it snappy but not visibly resorted.

Ref: p/68344926 b/13693117