Added navigation buttons in status bar for extended desktop

	modified:   core/java/android/provider/Settings.java
	modified:   core/res/res/layout/global_actions_silent_mode.xml
	new file:   packages/SystemUI/res/drawable-sw600dp-mdpi/gan_ic_sysbar_back.png
	new file:   packages/SystemUI/res/drawable-sw600dp-mdpi/gan_ic_sysbar_back_ime.png
	new file:   packages/SystemUI/res/drawable-sw600dp-mdpi/gan_ic_sysbar_home.png
	new file:   packages/SystemUI/res/drawable-sw600dp-mdpi/gan_ic_sysbar_menu.png
	new file:   packages/SystemUI/res/drawable-sw600dp-mdpi/gan_ic_sysbar_recent.png
	new file:   packages/SystemUI/res/layout-sw600dp/status_bar.xml
	modified:   packages/SystemUI/src/com/android/systemui/statusbar/BaseStatusBar.java
	modified:   packages/SystemUI/src/com/android/systemui/statusbar/phone/PhoneStatusBar.java