gnome3.gnome-control-center: add grilo-plugins

Opening a background change dialogue produces the following errors in the console:

    (gnome-control-center:27270): Grilo-WARNING **: 21:57:21.349: [registry] ../src/grl-registry.c:1354: Could not open directory '/nix/store/q8wdbr08617p3xqxdg8935p31fha020f-grilo-0.3.9/lib/grilo-0.3': Error opening directory “/nix/store/q8wdbr08617p3xqxdg8935p31fha020f-grilo-0.3.9/lib/grilo-0.3”: No such file or directory
    (gnome-control-center:27270): Grilo-WARNING **: 21:57:21.352: [registry] ../src/grl-registry.c:1461: Plugin 'grl-flickr' not available
    (gnome-control-center:27270): background-cc-panel-WARNING **: 21:57:21.352: Plugin “grl-flickr” not available

Apparently, there are no plugins in `grilo` package – everything is in `grilo-plugins`, so we need to add `grilo-plugins` to inputs. The setup hook will make the plug-ins available through an environment variable:

https://gitlab.gnome.org/GNOME/grilo/blob/grilo-0.3.9/src/grilo.c#L111-135

pkgs/desktops/gnome-3/core/gnome-control-center/default.nix

@@ -24,6 +24,7 @@
 , gnome-settings-daemon
 , gnome3
 , grilo
+, grilo-plugins
 , gsettings-desktop-schemas
 , gsound
 , gtk3
@@ -100,6 +101,7 @@ stdenv.mkDerivation rec {
     gnome-online-accounts
     gnome-settings-daemon
     grilo
+    grilo-plugins # for setting wallpaper from Flickr
     gsettings-desktop-schemas
     gsound
     gtk3