Improved ticker & bar animations.

The entire notification area fades out quickly before the
notification ticker appears, and fades back in when the
ticker is totally done.

This change has the side-effect of bringing back nice
animations for the notification icons when they appear by
themselves (at boot and when unlocking the device).

Bug: 3293680
Bug: 3018785
Change-Id: Id99cc20e6849f0f037fc9fba076243d362664478