PerformanceControlOptions revision

The PerformersOptionsForm in the
AssistantComposer is still completely redundant,
and should be removed. Do this soon!

PerformanceControlOption objects no longer
"cascade". They can now be an attribute of either
OutputVoice or OutputChord, and the
OutputChord settings update the current
OutputVoice settings as they occur.
The Study3Sketch2Algorithm now uses this new
paradigm. (There were problems with the old one,
relating to the indeterminacy of the order of
noteOns in a chord.)
MasterVolumes are treated similarly.
Refactoring PerformanceControlDef...

Renamed PerformanceControlDef to
InputControls and changed its behaviour slightly.
 If MidiChordDef.InputControls is not null, it is
now written to the SVG-MIDI file inside
score:midiChord, just above the
score:basicChords element.
Improved InputControls Volume options

InputControls.MaximumVolume is now cleanly
separated from the OutputVoice.MasterVolume.
InputControls now override completely

InputControls element are now always written
completely. These options are then valid
in the voice until further notice. This way it is
much easier to keep track of which options are
currently in force.
For test purposes in Study 3 sketch 2, added
pitchwheel->volume controls to bar 3, and
limited fade controls to bar 4.