Navring: Fix shortcut for uninstalled app

Fix NPE when the user uninstalls an app that was assigned to a navring
shortcut before.

Change-Id: I3f02fca73cb30e2edbb35d089ad127b35d8233c0
Power Menu: Update the Expanded Desktop drawable

Also add a proper "off" state.

Patch Set 2-4: Add to symbols.xml
Patch Set 5: Remove the useless extra sw600dp-xhdpi drawable

Signed-off-by: Paul Beeler <sparksco@gmail.com>