Instead of emitting InstrumentTrack::midiNoteOff() in destructor of
NotePlayHandle do this where it actually happens -> noteOff().
Fixes length of recorded notes when there's e.g. a long release.
Closes#378.
The volume of an InstrumentTrack is applied separately when post-processing
the audio buffer and is not related to MIDI processing. It therefore should
not be included into MIDI velocity calculation.
Closes#301.
Next big coding style update - this time all PlayHandle classes are
affected. Functions like done() and released() were renamed to
isFinished() and isReleased().
