chore: Significantly restructure folder layout

This moves the various projects from "type-based" folders (such as
"services" or "tools") into more appropriate semantic folders (such as
"nix", "ops" or "web").

Deprecated projects (nixcon-demo & gotest) which only existed for
testing/demonstration purposes have been removed.

(Note: *all* builds are broken with this commit)

ops/infra/nixos/dotfiles.nix

@@ -0,0 +1,27 @@
+# Bundle configuration files into a derivation.
+# I call this derivation dotfiles despite that not technically being true
+# anymore ...
+
+{ config, pkgs, ...}:
+
+let dotfiles = pkgs.stdenv.mkDerivation {
+  name = "tazjins-dotfiles";
+
+  srcs = [
+    ./dotfiles
+  ];
+
+  installPhase = ''
+    mkdir -p $out
+    cp ./* $out/
+  '';
+};
+in {
+  # /etc/ is a special place in NixOS!
+  # Symlinks that need to be created there must be specified explicitly.
+  environment.etc = {
+    "alacritty.yml".source    = "${dotfiles}/alacritty.yml";
+    "fish/config.fish".source = "${dotfiles}/config.fish";
+    "tmux.conf".source        = "${dotfiles}/tmux.conf";
+  };
+}