Revert "Revert "Refactor PanelView and NotificationPanelView into Controllers.""

This reverts commit da13c3fd.

This includes a fix for the original issue - an NPE in
NotificationPanelView.

Bug: 147295216
Change-Id: Id1a71b0e30aada460a70d738c5451e21dd412a7a
Test: atest SystemUITests