Bug Fix: Bug found while testing two-voice staves.

The main clef on the next system was being changed too early in
SvgSystem.AddSymbolsToSystems(...).
This bug turned up when debugging two-voice staves using a
variant of the Song Six score. Still not quite happy that I've found
all the two-voice bugs. Need to create a simple example.
Corrected text: Clytamnestra --> Clytemnestra
Beginning to realise ties.

Added tieHook and shortTie definitions to the StandardSymbolSet.
These are written to the <defs> section in each SVG score page.
Ties not implemented after all, removed unreachable code.

Decided not to implement ties after all, so removed the
corresponding code from StandardSymbolSet.cs
Removed unreachable code from SongSixAlgorithm.cs.
Added the repeatMoments attribute to MidiChordDef
Added repeats input to palettes.

Palettes now save and load PaletteMidiChordDef.Repeat attributes.
And, when creating a score, these values are written to the ChordDefs.
The ChordDef.repeat attribute can be omitted in the score, in which
case it is true by default.
Added stub code for Study 4

The object of this exercise is to write a new piece
using an improved version of the VoiceDef class.
1. Added a copy of VoiceDef.cs to the SongSix
folder, and renamed it SongSixVoiceDef.cs.
Refactored all the Song Six code to use this new
SongSixVoiceDef class.
2. The original VoiceDef class still exists, and one
of its constructors is still used by Study 3 sketch.
But this VoiceDef is going to change (probably
quite drasically) to take account of the Study 4
algorithm. I want to make the process of
composing easier by defining positions in the
score symbolicly (i.e. names instead of numbers).
3. The file Study4Algorithm.cs exists, but is simply
a cannibalised copy of the original
SongSixAlgorithm.cs which has been crudely
edited so that it compiles.
4. The Study4.mkss file exists, but needs changing.
Small Bug Fix in VoiceDef indexer.set

SetMsPositions must be called whenever the
_uniqueMidiDurationDefs list has changed.
Also fixed in SongSixVoiceDef.
Added Performer Options Form

This loads from, but does not yet save to .mkss
files. Everything is working on the Form, except
saving.
Performer Options are now saved in .mkss files

The options can now be changed and reloaded.
If a score does not yet have performer options,
a default set is provided (with the right number
of channels).