add appimage-builder recipe
Add appimage-builder recipe and gitlab-ci instructions to pack Kstars as an AppImage.
It may need some tuning to reduce the bundle size, but I'm not familiar enough with the software. You may check the appimage-builder.yml and remove any unneeded dependency.
Also I'm taking libraw20 binaries from the system, if it's available in a ppa it would be better to fetch it from there.
Edited by Alexis Lopez Zubieta