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/desktop.nix

@@ -0,0 +1,82 @@
+# Configuration for the desktop environment
+
+{ config, lib, pkgs, ... }:
+
+let emacs = import ./emacs.nix { inherit pkgs; };
+screenLock = pkgs.writeShellScriptBin "screen-lock" ''
+  find ${pkgs.wallpapers} -name "*.png" | shuf -n1 | xargs i3lock -f -t -i
+'';
+in {
+  # Configure basic X-server stuff:
+  services.xserver = {
+    enable = true;
+    layout = "us,no";
+    xkbOptions = "caps:super, grp:shifts_toggle, parens:swap_brackets";
+    exportConfiguration = true;
+
+    # Give EXWM permission to control the session.
+    displayManager.sessionCommands = "${pkgs.xorg.xhost}/bin/xhost +SI:localuser:$USER";
+
+    # Use the pre 18.09 default display manager (slim)
+    displayManager.slim.enable = true;
+  };
+
+  # Add a shell script with random screen lock wallpaper selection
+  environment.systemPackages = [ screenLock ];
+
+  # Apparently when you have house guests they complain about your screen tearing!
+  services.compton.enable = true;
+  services.compton.backend = "xrender";
+
+  # Configure desktop environment:
+  services.xserver.windowManager.session = lib.singleton {
+    name = "exwm";
+    start = ''
+      ${emacs}/bin/emacs --eval '(progn (server-start) (exwm-enable))'
+    '';
+  };
+
+  # Configure Redshift for Oslo
+  services.redshift = {
+    enable = true;
+    latitude = "59.911491";
+    longitude = "10.757933";
+  };
+
+  # Configure fonts
+  fonts = {
+    fonts = with pkgs; [
+      corefonts
+      font-awesome-ttf
+      input-fonts
+      noto-fonts-cjk
+      noto-fonts-emoji
+      powerline-fonts
+      helvetica-neue-lt-std
+    ];
+  };
+
+  # Configure random setting of wallpapers
+  systemd.user.services.feh-wp = {
+    description = "Randomly set wallpaper via feh";
+    serviceConfig = {
+      Type             = "oneshot";
+      WorkingDirectory = "${pkgs.wallpapers}/share/wallpapers";
+
+      # Manually shuffle because feh's --randomize option can't be restricted to
+      # just certain file types.
+      ExecStart = "${pkgs.bash}/bin/bash -c '${pkgs.fd}/bin/fd -atf | shuf | head -n1 | ${pkgs.findutils}/bin/xargs ${pkgs.feh}/bin/feh --bg-fill'";
+    };
+  };
+
+  systemd.user.timers.feh-wp = {
+    description = "Set a random wallpaper every hour";
+    wantedBy    = [ "graphical-session.target" ];
+    partOf      = [ "graphical-session.target" ];
+
+    timerConfig = {
+      OnActiveSec     = "1second";
+      OnUnitActiveSec = "1hour";
+    };
+  };
+}