Miscellaneous changes

This is a grab bag of small things that help improve functionality and sheet music appearance.

Support color-coded chords with multiple voices.  Currently, intervals between notes of a chord that are in different voices cannot be calculated.  This may not be a quick fix.

Key signatures in WYSIWYP format .  This may or may not be a good idea.  One of the main goals of the notation is to eliminate the need to know the key signature in order to implicitly identify the sharps and flats because the noteheads define them explicitly.  However, there may be some students who do want to see a key signature just to be aware of keys and to learn them.  This would not change the staff display of the notes, just add the signature in front of the staff similiar to Traditional Notation.  In this implementation, the Key Signature should conform to the WYSIWYP notation, i.e., use WYSIWYP noteheads instead of the traditional symbols for sharp and flat.  Probably a fair amount of code to implement.

Pickup measure without measure number.  This is to match the Traditional Notation convention.