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 fcc901c.

Change-Id: I7aa85f7c8442c45d17e42cac7823dfe93e3f24c1

Conflicts:

core/java/android/provider/Settings.java