Seperate flatpak-system packages and flatpak-user packages

[dnkmmr69420]

You know how there is nix-default and nix-user, there should be flatpak-user and flatpak-system. Maybe this can be configurable too and maybe even a config option to have nix package numbers merged. Fast Fetch does this

[hykilpikonna]

Done! Now you can use --package_separate flag to separate system and user packages.