Switch back to Vim

- Change default editor back to vim since doom-emacs is broken at the
  moment
- Conditionally include emacs or vim nix files in configuration.nix
- User username to find dwm-flexipatch path on system
- Add tree and btop to miscellaneous system packages
- Add some cli tools like just and git to home-manager packages
- Add more XDG env vars for config and cache

user/development/cli.nix

@@ -0,0 +1,8 @@
+{ config, lib, pkgs, ... }:
+
+{
+  home.packages = (with pkgs; [
+    git
+    just
+  ]);
+}