Move system/home/default.nix into system/default.nix,
system/home/desktop/default.nix into system/desktop.nix to reduce
unnecessary duplication. Moved everything in home/desktop up to home/
and adjusted paths accordingly. Moved wallpapers up to system/ since
it makes sense with where it's used.
Merge allowUnfreePredicate into single place again since it seems to
override rather than combine if used multiple times.
Install NoMachine on all machines again by default.
Move stylix config up to flake.nix as config wouldn't build without it,
also move wallpapers directory up to top level to match
Only enable git-sync where it's defined, rather than in home/default.nix
Evie Litherland-Smith
