App sidebar: some adjustments

- Cleanup
- fix disappearing appbar on changing appbar position
- may fix endless FC on changing appbar contents

Change-Id: I7667e60878c07b7c722dbd2bd5c2fd69bbbdda78

Conflicts:
	packages/SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java
	packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java