PIE: Panels are centered and have margins

Change-Id: I596f21c584b059465098b6245d506be276813d20

Conflicts:
	packages/SystemUI/res/values/dimens.xml
	packages/SystemUI/src/com/android/systemui/statusbar/PieControl.java
	packages/SystemUI/src/com/android/systemui/statusbar/PieControlPanel.java
	packages/SystemUI/src/com/android/systemui/statusbar/view/PieStatusPanel.java