Wallpaper Overscroll and Transparent NavBar

Now possible to offset wallpaper windows by more than the size of the wallpaper
and add added a transparent mode to the NavigationBar

Change-Id: I2b0f1129a4cf73b8def35abb7072d0472a9cc972

Conflicts:

	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java
	services/java/com/android/server/wm/Session.java