clean up code
Add two-state back to ControlLogpotmeterBehaviorback. For some reason I believed this was unused but the volume sliders use it.
Wait for the EngineWorkerScheduler thread to complete before destruction. This fixes a crash-on-exit that I believe is caused since we no longer have a SyncWorker.
Fix hang-on-exit deadlock in VinylControlManager. This is triggered by the recent collapsing of ControlObject and ControlObjectThread.