xmp: \label as arg to \fullPageMusicExample

The label as argument to the printing commands has slightly been redefined.
Now one has to provide '\label{' oneself instead of only the label content.
This ensures that there actually is a real label in the source at the correct place
xmp: Doc Progress
Implement \parttitle and \chaptertitle

Two commands (similar to starred sectioning commands) that should be used instead of a title (for subfiles).