partial fix for #33726: avoid wrong partnames with SATB closed score

due to the '/' in the partname "Soprano/Alto" and "Tenor/Bass", partnames get
truncated to which leads to part names of "Alto" and "Bass".
Change the offedning "/" to "+" in the templates.
See http://musescore.org/en/node/33726#comment-142726
Merge pull request #1400 from Jojo-Schmitz/templates

  partial fix for #33726: avoid wrong partnames with SATB closed score