Make navigation bar ready for per-user configuration.

Also clean it up a bit.

Change-Id: Ic10bd161fce53bf30048a0cb927dcf1e2bfa7774

Conflicts:

	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java
	packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java
Revert "Make navigation bar ready for per-user configuration."

This reverts commit 03c7a2fd394ad730edb06a18b50900864ebc8573.