[1/2] TrafficMeter: added option for auto-hiding on inactivity

Together with inactivity threshold

Thanks to @C3C0 for the code

TrafficMeter: fix auto hiding when Bytes is set as the unit

Change-Id: I3d3cdfb61b1cbbfcaf4c6f5043409946bb69ec57

Conflicts:
	core/java/android/provider/Settings.java