framework: Bring back the status bar activity indicators for mobile data and wifi

* adds a setting for this as well as reverting the following commit:

Reverts "Remove signal/wifi activity indicator icon overlays."

This reverts commit fcc901c10bffdfb9c6b31e676dec36b47d949979.

Change-Id: I7aa85f7c8442c45d17e42cac7823dfe93e3f24c1

Conflicts:
	core/java/android/provider/Settings.java
	packages/SystemUI/res/layout/signal_cluster_view.xml
	packages/SystemUI/src/com/android/systemui/statusbar/SignalClusterView.java
	packages/SystemUI/src/com/android/systemui/statusbar/policy/NetworkController.java