Clean up save, save as, open, export, etc. dialogs

to consistently not use "Compressed", use "Uncompressed" for the
MuseScore formats and use "File" instead of "Format" for all or them.
Also remove the last remainder of the old msc format.
Merge pull request #1326 from Jojo-Schmitz/pre-translation

consistently remove "compressed", add "uncompressed" and use "File(s)" rather than "Format"