SystemUI demo mode.

Control the status bar visuals via a simple intent protocol.
Useful for comprehensive visual testing reachable assets
and the various bar modes.

Protected behind a global system setting.  To enable:
  adb shell settings put global sysui_demo_allowed 1

Remove obsolete sync failing asset, and tighten up
BluetoothController to represent reality.

Bug:10502089
Change-Id: I28443af3d6b22fcb7b367ef70e1d95fc23ebd407