revert(glittershark): "Temporarily skip grfn's subtree"

This reverts commit 475d41f698. I'd like
my derivations back, please.

Changes necessary to get this working:

- Don't depend on `nixpkgs` being in the NIX_PATH for my website - it's
  not necessary anyway since emacs 27 is mainline now
- .skip-subtrees on things that shouldn't be evaluated anyway
- Get rid of system/pkgs, and move the one thing in there that *wasn't*
  already in third_party (alsi) to third_party
- Drop notifymuch for now - it's not working, and I'll probably get it
  landed in nixpkgs before I manage to get it working
- Add __readTree = true to my systems so they get built.
- explicitly disable ci for xanthous, which is failing to build and had
  been omitted previously

Change-Id: I20f5e81d6eb7ffe040091a08d75d0cb15304f707
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1864
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

third_party/alsi/OWNERS

@@ -0,0 +1,3 @@
+inherit: true
+owners:
+ - glittershark

third_party/alsi/default.nix

@@ -0,0 +1,25 @@
+{ pkgs, ... }:
+
+with pkgs;
+
+stdenv.mkDerivation {
+  name = "alsi";
+  pname = "alsi";
+  version = "0.4.8";
+
+  src = fetchFromGitHub {
+    owner = "trizen";
+    repo = "alsi";
+    rev = "fe2a925caad38d4cc7afe10d74ba60c5db09ee66";
+    sha256 = "060xlalfclrda5f1h3svj4v2gr19mdrsc62vrg7hgii0f3lib7j5";
+  };
+
+  buildInputs = [
+    (perl.withPackages (ps: with ps; [ DataDump ]))
+  ];
+
+  installPhase = ''
+    mkdir -p $out/bin
+    cp alsi $out/bin/alsi
+  '';
+}