Add GNOME

- Add config option to switch between window managers / desktop environments
- Remove systemPackages attribute when a service or program attribute is available
- Add GNOME to gui

system/hardware/bluetooth.nix

@@ -1,7 +1,6 @@
 { config, lib, pkgs, ... }:
 
 {
-  environment.systemPackages = [ pkgs.blueman ];
   hardware.bluetooth.enable = true;
   services.blueman.enable = true;
 }