Revert "remove navigation bar customization"

This reverts commit 4b58b80587a3e562bcc516940c02c8435a417541.

Conflicts:
	packages/SystemUI/res/values/ras_strings.xml
	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarTransitions.java
	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java
	packages/SystemUI/src/com/android/systemui/statusbar/policy/KeyButtonView.java

Conflicts:
	packages/SystemUI/res/values/ras_strings.xml