Adds dummy HomeGestureTutorialFragment.

 - Adds a new launch target in Dev options
 - Moves Back handling to the parent TutorialFragment
   (so all Tutorials can handle it as necessary)
 - Currently uses a dummy translating rectangle in
   place of a proper hand animation
 - No actual home gesture recognition is in place yet

Test: Manual
Bug: 148542211
Change-Id: Ic5a545eb9f5003914803272c8ffe367220d63336