QuickSettings : Cleanup receivers/observers

This patchset borrows the idea of a central observer/receiver
from powerwidgets. This way cleanup is a lot easier.

Change-Id: I09ff3118cbc1137e2569dcd3e07acb2a3b083eca

Conflicts:
	packages/SystemUI/src/com/android/systemui/quicksettings/ProfileTile.java