SupportLeanbackShowcase: bring gradle, build tools, lib up to date am: 15f5a3351f am: dcba115971
am: 731ad2a79f

* commit '731ad2a79f656b6c9ec71e2ce37df1ca5d084bdc':
  SupportLeanbackShowcase: bring gradle, build tools, lib up to date

Change-Id: Id7bbba0dc1d5ace5a473376ce3bf66108317c141