Add localtime package and nixos module

Simple daemon for keeping system timezone up-to-date via geoclue2.

Sadly i3 status needs to be restarted for timezone changes.

pkgs/tools/system/localtime/default.nix

@@ -0,0 +1,22 @@
+{ stdenv, go, systemd, polkit, fetchFromGitHub, m4 }:
+
+stdenv.mkDerivation {
+  name = "localtime-2017-11-07";
+
+  src = fetchFromGitHub {
+    owner = "Stebalien";
+    repo = "localtime";
+    rev = "2e7b4317c723406bd75b2a1d640219ab9f8090ce";
+    sha256 = "04fyna8p7q7skzx9fzmncd6gx7x5pwa9jh8a84hpljlvj0kldfs8";
+  };
+  
+  buildInputs = [ go systemd polkit m4 ];
+
+  makeFlags = [ "PREFIX=$(out)" ];
+
+  meta = {
+    description = "A daemon for keeping the system timezone up-to-date based on the current location";
+    homepage = https://github.com/Stebalien/localtime;
+    platforms = stdenv.lib.platforms.linux;
+  };
+}