Prevent some master sync party-stoppers:
* Deck passthrough activates -> sync disables
* Track ejected -> if master, sync disables, otherwise no change.
* Beatgrid on track cleared or becomes empty (0BPM) -> if quantize enabled, disable it (that's all we can do from bpmcontrol)
Prevent another party stopper
* If track is loaded or unloaded on explicit master, hand off.
Merge pull request #128 from ywwg/master_sync-party_stoppers

Prevent some master sync party-stoppers