Make an official Flatpak on Flathub

(#948) Feature Shipped packaging

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Comment by @xxhinotorixx
RexSystem 1 vote originally by @xxhinotorixx on GitHub
continuation about me trying to pack it: for right now i am stuck with a problem, as per flatpak documentation: setting the disable-lfs flag in the git source SHOULD make it stop trying to pull lfs files, while the primary download succeeds, when it gets to the build phase, it starts updating files, which includes pulling lfs files, which then makes it fails
I had the same problem. In the end I made the Flatpak out of the AppImage.