iOS 13 Crash Fixes

[sieren]

Hey,

Please read each commit in the history to see whats going on.

TL'DR:

• Moved a lot of audio-engine functionality that was called from the View Code into the Conductor.
• Instantiation of Engine and Conductor is now happening in AppDelegate so it's guaranteed to only be called once
• AudioPlot is also a part of the Conductor now, better solutions are appreciated because it's technically UI Code (with an Engine dependency)
• Reinstantiated the Constraints from @analogcode previous experiments
• AudioBus MIDI Code is now part of the Conductor and the Manager is a delegate to incoming AB Midi messages.

Please test this if possible, especially the AudioBus related stuff.