there is no wf-only "controls" anymore.
migrate piano context menu events to commands.
migrate track selector events to commands.
moved game controller related code to model.
sanitize dialog API.
migrate PianoRoll events to commands (kind of; it's still nasty)
migrated TrackSelector events to commands.
move playing feature in MainForm to model.
move "ensure visibility on piano roll" code to model.
hand cursor was actually provided by app, not system.