mopidy-local: init at 3.1.1

Mopidy-Local is the successor to Mopidy-Local-SQLite and
Mopidy-Local-Images, which are already packaged. I had to make
gobject-introspection a propagated build input, otherwise
Mopidy-Local can't import Mopidy.

pkgs/applications/audio/mopidy/default.nix

@@ -14,6 +14,8 @@ let
 
     mopidy-gmusic = callPackage ./gmusic.nix { };
 
+    mopidy-local = callPackage ./local.nix { };
+
     mopidy-local-images = callPackage ./local-images.nix { };
 
     mopidy-local-sqlite = callPackage ./local-sqlite.nix { };