- check appimage with Arch and --capabilities - this catches segfault
with incompatible jack implementation in bundle and system
(pipewire-jack package needed)
- use empty directory for container build (instead of ".") also for
Ubuntu (would not needlessly copy contents of current directory to
Docker daemon)
SDL_mixer has some nasty dependency on JACK so remove it altogether
since it is perhaps seldom used (the MIDI playback may be added later
eg. as a standalone audio capture).
(see GH discussion #241)
