follow up fix for #22904

mostly cosmetic, but it seems better to show the user upfront what (s)he
will get when generating parts.
fix #37696: sanitize filenames when exporting parts

and while at it make the "Score_And_Parts" translatable.
Also force the score's name as the first part of the name of the
exported parts, regardless of which tab is the active one.
Merge pull request #1411 from Jojo-Schmitz/part-export

Part export improvements