Add gnome shell extensions module

hm_modules/gnome_shell.nix

@@ -0,0 +1,29 @@
+{ pkgs, ... }:
+
+let
+  gnomeExtensions = with pkgs.gnomeExtensions; [
+    babar
+    caffeine
+    dash-to-dock
+    dash-to-panel
+    # dash-to-plank
+    # devbar
+    dock-from-dash
+    # espresso
+    # focus
+    freon
+    gamemode
+    # git
+    gtile
+    # jiggle
+    just-perfection
+    # keyman
+    # tray-icons
+    unite
+    # vitals
+    user-themes
+  ];
+in
+{
+  home.packages = [ pkgs.gnome.gnome-tweaks ] ++ gnomeExtensions;
+}