Always disable() through SBMS; watch date.

Touching StatusBar.disable() directly can make the cached value over
in StatusBarManagerService stale.  Instead, dispatch DISABLE_BACK
through setSystemUiVisibility() on tablets; it's unused on phones.

Also DISABLE_NOTIFICATION_TICKER when showing secure lockscreen, and
watch for TIME_CHANGED in DateView.

Bug: 5255469
Bug: 5242677
Change-Id: I4efaf9799b2f229f49d7024da5dafceacd5e08bb