Add wireless display selection support to MediaRouter.

* Adds the new route type LIVE_VIDEO

* Wireless displays support both LIVE_VIDEO and LIVE_AUDIO, making
  wireless display routes valid selections in when apps make selecting
  live audio routes available.

* MediaRouter will only report/manipulate wireless displays that have
  already been paired at the system level.

Bug 7177920

Change-Id: Ic221b8687d77b4c0df9801c396b74870e86206e9