services: add sabnzbd

Its configuration isn't declarative :-(.

Notably, the port needs to be changed from '8080' to '9090' in its
configuration file (at '/var/lib/sabnzbd/').

services/default.nix

@@ -8,6 +8,7 @@
     ./media.nix
     ./nginx.nix
     ./pirate.nix
+    ./sabnzbd.nix
     ./transmission.nix
   ];
 }