SystemUI: add customizable navigation bar

Change-Id: Ibad1ecf52c7db0ac352892aed7529de68476c092
Signed-off-by: Roman Birg <romanbirg@gmail.com>

Conflicts:
	core/res/res/values/pac_strings.xml
	packages/Keyguard/src/com/android/keyguard/KeyguardSelectorView.java
	packages/SystemUI/res/layout-sw600dp/navigation_bar.xml
	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java
	packages/SystemUI/src/com/android/systemui/statusbar/policy/KeyButtonView.java
	packages/SystemUI/src/com/android/systemui/statusbar/policy/activedisplay/ActiveDisplayView.java