Migrate away from appdirs

[paddatrapper]

Debian bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1067970

Please migrate away from appdirs. It is dead upstream and is going to be removed from Debian. platformdirs is a recommended fork with a similar API that should be straightforward to migrate to. Documentation: https://platformdirs.readthedocs.io/en/latest/

[ObjectBoxPC]

From what I can tell, the appdirs APIs that this program uses are the same in platformdirs, so it would be quite literally a simple find and replace across the code as well as build scripts and localizations.

[SpotlightKid]

I'll tag a new release tomorrow or next week.

[hosiet]

@SpotlightKid It looks like we still miss a tag of v19 in https://github.com/jack-mixer/jack_mixer/tags . Tagging a release would be beneficial.

[SpotlightKid]

Yeah, sorry, I was hoping I can get PR #167 also into this release, but I guess I have postpone that. I'll do a release now.