Keep VirtualBox out of my home dir

hm/common.nix

@@ -386,6 +386,15 @@ in
     };
   };
   home = {
+    activation = {
+      # Prevent Virtualbox from creating a "VirtualBox VMs" folder in $HOME
+      setVirtualboxSettings = lib.hm.dag.entryAfter [ "writeBoundary" ] ''
+        if command -v VBoxManage > /dev/null
+        then
+            VBoxManage setproperty machinefolder ${config.xdg.dataHome}/virtualbox
+        fi
+      '';
+    };
     stateVersion = "23.11";
     language = {
       base = "en_US.UTF-8";
@@ -411,6 +420,11 @@ in
       zsh-history-substring-search
       powerline-go
 
+      # nix utils
+      nix-diff
+      nix-tree
+      nix-output-monitor
+
       # terminal essentials
       file
       moreutils