Staffless neume glyph scaling

Calculate the global glyph scaling paramater using neumes instead of the
intrastaffline distance.
Update staffless neumes SVG

Added tractulus neume and removed the symbolic link to the development
SVG document.
Move GUI interaction code

Now the GUI class just creates the interface elements and a separate
class handles the interaction with glyphs on the drawing surface since
the interaction code is document dependent. Still need to code up
interaction with staffless neumes.