Launcher: Add customization wallpaper

Add control WallpaperChooser to select Launcher resource
or select carrier's wallpaper resouce.

Change-Id: I7915b6e6f9537f0e96715a611d77d4db8bc0f694
Fix - Workspace background gradient

Repro:
 - Open App Drawer
 - Launcher any app
 - Press back (User should be returned to the App Drawer)
 - Press back again (User should be returned to the Home Screen)
 - Note gradient near status bar (Home Screen gradient is missing!)
 - Press home
 - Note Home Screen gradient reappears

Change-Id: Ib24d94c2deba06f872f42bfffff78317844dd731