later:
- auto-volume-from-loop gets lost in pan-flute instrument export
- fix error handling for WavSet::save() and others
- combobox should support scroll wheel
- multiple bank support
- better indicator for outdated WavSources

SVEN:
- keep playing if only loop points are edited
- zoom center at zoom marker
- continuation mode: either
  - (1) on note off: store position, restart there
  - (2) use control signal as offset into loop
  -     use tempo mode
