Media: Add group id for media router to sync

This CL adds MediaRouter.setRouterGroupId() methods to set the "group id"
of a media router.

Media routers that have the same group id synchronize their
selected route.

For example, if System UI and Settings use the group id, you can see
"connected" status from System UI even if the cast begins from Settings
, and vice versa.

Bug: 112826114
Bug: 131385091
Bug: 130345243

Test: manually w/ setting the same group id for Settings and System UI.
Change-Id: I9d4e061b57f52d7b2bec622b5f02068f3d11c133