[WIP] GEL Integration

Launch search from extra panel to mimic Google Launcher. Patch is for
reference only, needs a lot of cleanup (animations, fix home behavior, etc).

PS2: Check for global search presence before showing custom panel. Also
     use proper ASSIST intent (so we don't show keyboard).
PS3: Fix home screen return action

Todo: Animations/Transitions

Change-Id: Id808d4ebfe374c8743660496e57a6b6cf1192f32