Update NSSL footer views within NSSL

Instead of relying on NotificationPanelView to relay information to the
NSSL, the NSSL's Controller can update its footer views (including the
empty notification shade view "No notifications" and the "Manage" and
"Clear all" buttons) by itself.

Test: manual
Change-Id: I127839fe83159089fe915739549c0a29c2e25285