Update signal, wifi, battery assets + global dimming.

Global status bar dimming is now 75%.

Signal/wifi: use problem color if not fully connected.

Battery: frame 40% white, charge level = white, new hollow bolt.
  (hollow bolt simulated for now until we can draw it in code)

Update ic_notification_overlay, all sizes.

Workaround animation bug on tablets.

Bug:10502089
Change-Id: I10f979b7a48ccb1bc94022d8c189ec216283dbe6