clean up SourceFactory - amend to beb22869edd2c
reset midi synth (panic) when seeking or re-starting audition
tweak reasonable synth:

* prevent denormals / cut low volume
* reduce default amplitude of fundamental
reset state-tracker (amend to cd971bb22e58f02)
display some midi file info (amend to d4c39ba10c68151)
prepare midi-audition synth plugin config, incl no plugin external synth