nixos: add quickshell/waybar/taffybar modules

- Switch taffybar input to the local submodule
- Add caelestia quickshell (home-manager module)
- Make waybar/taffybar mutually exclusive, defaulting based on xmonad
- Move tray ordering and status notifier watcher config into the right modules

nixos/configuration.nix

@@ -33,14 +33,17 @@
     ./plasma.nix
     ./postgres.nix
     ./rabbitmq.nix
+    ./quickshell.nix
     ./secrets.nix
     ./ssh.nix
     ./sni.nix
     ./syncthing.nix
+    ./taffybar.nix
     ./tts.nix
     ./user-specific.nix
     ./users.nix
     ./vscode.nix
+    ./waybar.nix
     ./wsl.nix
     ./wyoming.nix
     ./xmonad.nix