Fix status bar brightness control when on secure lock screen

When the notifications panel is disabled no views are handling touch events
on the status bar, so we see nothing beyond each ACTION_DOWN. Intercept touch
events when needed specifically for brightness control.

Also recycle VelocityTracker when we're not using it, as per its documentation.

Change-Id: I84d4c788bcdb1e05244710aca933d97e3e60d1b5

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java