CastTile : Cosmetic changes to the cast tile UX.

- Change the tile title to "Screen Cast".
- Always show the tile title as a primary label, and show
  the casting or projection device as the secondary label.
- Also fixes an issue where the cast tile would show as disabled
  when WiFi wasn't connected, despite the fact that the tile may
  have been displaying an in-progress projection session.

Test: manual
Bug: 124753835

Change-Id: I15f9c0a80d288e5d9a77e87fd1f3135033fdb873