Bunch More Packages

- Add thunar file manager to dwm
- Add nitrogen wallpaper setter to dwm
- Add rclone, sweethome 3D, mangal, qalculate-gtk, octave, and
  qbittorrent packages

user/productivity/math.nix

@@ -0,0 +1,8 @@
+{ config, lib, pkgs, ... }:
+
+{
+  environment.systemPackages = with pkgs; [
+    qalculate-gtk
+    octave
+  ];
+}