proper merging for #12008 and #12138
use multimap for spanner list
slur direction is down by default for grace notes
fix slur for grace note
Fix for issue #8027

Missing note MIDI #94 has now been fixed in the soundfont. The soundfont
has also been converted to SF3 format. Embedded references to the
filename have also been edited.
Merge pull request #387 from ChurchOrganist/Fix-for-#8027

Fix for issue #8027
fix cut&paste of slured grace notes
fix copy&paste for spanner
fix #21601: Pasting multi-stave notes that cross to non-existant stave causes crash
make tests more verbose in case of failure
fix #21600: Rests not produced for other stave when pasting multi-stave notes with differing values
fix grace notes in parts