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)

infra/nixos/packages.nix

@@ -1,132 +0,0 @@
-# This file contains configuration for packages to install.
-# It does not contain configuration for software that is already covered
-# by other NixOS options (e.g. emacs)
-
-{ config, pkgs, ... }:
-
-let
-  fetchChannel = { rev, sha256 }: import (fetchTarball {
-    inherit sha256;
-    url = "https://github.com/NixOS/nixpkgs-channels/archive/${rev}.tar.gz";
-  }) { config.allowUnfree = true; };
-
-  # Channels last updated: 2018-10-10
-  #
-  # Instead of relying on Nix channels and ending up with out-of-sync
-  # situations between machines, the commit for the stable Nix channel
-  # is pinned here.
-  stable = fetchChannel {
-    rev    = "d96c7a356383302db4426a0d5a8383af921d964f";
-    sha256 = "0hlhczh3m077rwrhp4smf3zd2sfj38h2c126bycv66m0aff0gycn";
-  };
-
-  # Certain packages from unstable are hand-picked into the package
-  # set.
-  unstable = fetchChannel {
-    rev    = "32bcd72bf28a971c9063a9cdcc32effe49f49331";
-    sha256 = "1f74m18r6xl9s55jbkj9bjhdxg2489kwjam4d96pf9rzq0i1f8li";
-  };
-in {
-  # Configure the Nix package manager
-  nixpkgs = {
-    config.allowUnfree = true;
-    # To use the pinned channel, the original package set is thrown
-    # away in the overrides:
-    config.packageOverrides = oldPkgs: stable // {
-      # Store whole unstable channel in case that other modules need
-      # it (see emacs.nix for example):
-      inherit unstable;
-
-      # Backport Exa from unstable until a fix for the Rust builder is
-      # backported.
-      #
-      # https://github.com/NixOS/nixpkgs/pull/48020
-      exa = unstable.exa;
-
-      wallpapers = import ./pkgs/wallpapers.nix;
-      pulseaudio-ctl = import pkgs/pulseaudio-ctl.nix;
-    };
-  };
-
-  # ... and declare packages to be installed.
-  environment.systemPackages = with pkgs; [
-    # Default nixos.* packages:
-    alacritty
-    binutils-unwrapped
-    chromium
-    curl
-    direnv
-    dnsutils
-    dotnet-sdk
-    evince
-    exa
-    extremetuxracer
-    fd
-    file
-    firefox-unwrapped
-    fish
-    gcc
-    git
-    gnumake
-    gnupg
-    google-cloud-sdk
-    gopass
-    hicolor-icon-theme
-    htop
-    i3lock
-    iftop
-    jq
-    kontemplate
-    kubernetes
-    lispPackages.quicklisp
-    lxappearance-gtk3
-    manpages
-    maven
-    mono
-    mq-cli
-    msmtp
-    ngrok
-    notmuch
-    numix-cursor-theme
-    numix-gtk-theme
-    numix-icon-theme
-    offlineimap
-    openjdk
-    openssl
-    openssl.dev
-    pass
-    pavucontrol
-    pkgconfig
-    pulseaudio-ctl
-    pwgen
-    ripgrep
-    rustup
-    sbcl
-    screen
-    siege
-    spotify
-    stdmanpages
-    systemd.dev
-    tdesktop
-    terraform
-    tig
-    tmux
-    tokei
-    transmission
-    tree
-    units
-    unzip
-    vlc
-    xclip
-    xfce.xfce4-screenshooter
-
-    # Haskell packages:
-    cabal-install
-    ghc
-    hlint
-    stack
-    stack2nix
-    haskellPackages.stylish-haskell
-    haskellPackages.yesod-bin
-  ];
-}