Cleaning up references to mDragView after reordering Workspaces

Change-Id: I480142b4714034c5579232a6a0d30f3aecb687ac
Trebuchet: add lockscreen wallpaper picker

Change-Id: Ic4f2589924a3c61b676db907f08108286dc45c29
Signed-off-by: Roman Birg <roman@cyngn.com>