Repeat improvements

• \repeat volta alternative endings no longer create invisible bar lines. This may affect line breaking, horizontal spacing, and VoltaBracket extent where an alternative begins or ends without a bar line. In the case of an undesired change, try adding \bar "" or another command that creates a BarLine at that point.
• Using the new printInitialRepeatBar property, it is possible to make a start repeat bar line automatically printed even at the beginning of the piece.

  

• The volta number position relative to the the volta bracket can now be adjusted with the volta-number-offset property of VoltaBracket.