fix #19441
Merge pull request #157 from Jojo-Schmitz/master

fix #19441
removed mxmlOff (prepare for fixing #19459)
#15899: support multi-staff parts with figured bass elements
#15899: support figured bass extend elements
#16057: prepare for MusicXML export of fret diagrams
Merge pull request #160 from lvinken/musicxml-fixes

Musicxml fixes