add an observer to update signal lte and 4g icons (2/2)

  - remove the need for the systemui restart

Change-Id: I632c4999747fd7e45a1a51519124b8d5db583e6b
Settings: option to hide signal bars (2/2)

Change-Id: I86847055fbd042291c90aae252c5d071aac125a6