Fallback to ultrasonic if smart watch is disconnected

From Fei Kuan on 2017/03/25 03:27:52 +0000

I occasionally find my smart watch disconnected during sleep tracking, leaving the graph blank in the morning. As ultrasonic tracking is more stable now, I think should automatically fall back to ultrasonic when the watch is disconnected as people usually put their phone near their bed anyway.

Copied from original feature request: http://urbandroid.uservoice.com/forums/264867-sleep-as-android/suggestions/18721357-fallback-to-ultrasonic-if-smart-watch-is-disconnec