Move sway to desktop/sway and move other packages under programs/sway
up a level to programs/desktop, add niri config to desktop/niri and
refactor common desktop imports into desktop/default.nix that also
imports (for now at least) sway and niri modules
Move wallpapers into programs/desktop since that's where they're
needed anyway
Add helper script to call swaybg with arguments
Evie Litherland-Smith