make everything more modular + basic kitagawa config using gnome

modules/desktop-environments/gnome.nix

@@ -0,0 +1,20 @@
+{
+  config,
+  pkgs,
+  ...
+}: {
+  services.desktopManager.gnome.enable = true;
+
+  # To disable installing GNOME's suite of applications
+  # and only be left with GNOME shell.
+  services.gnome = {
+    core-apps.enable = false;
+    core-developer-tools.enable = false;
+    games.enable = false;
+  };
+
+  environment.gnome.excludePackages = with pkgs; [
+    gnome-tour
+    gnome-user-docs 
+  ];
+}