Apps, refactor, clean up, remove librewolf

Refactors to use app.nix for easier extension.

Removes librewolf from host, as it makes more sense on the user every
time.

nixosModules/apps/virtualbox/default.nix

@@ -1,15 +0,0 @@
-{ config, pkgs, lib, ... }:
-
-{
-  options.virtualbox = {
-    enable = lib.mkEnableOption "Enables virtualbox";
-    extra-users = lib.mkOption { default = []; };
-  };
-
-  config = lib.mkIf config.virtualbox.enable {
-    virtualisation.virtualbox.host.enable = true;
-    users.extraGroups.vboxusers.members = [
-      config.user.name
-    ] ++ config.virtualbox.extra-users;
-  };
-}