Cleanups

Hide GDBus from RTKit API
Remove register node from dbus API
Add signal
Add object and register objects in the registry
Add some preregistered types to the registry
Let the daemon listen to the registry

pinos/server/dbus-client-node.c

@@ -267,7 +267,7 @@ make_node (PinosDaemon *daemon, SpaHandle **handle, SpaNode **node, const char *
       return res;
     }
     if ((res = spa_handle_get_interface (*handle,
-                                      spa_id_map_get_id (daemon->map, SPA_NODE_URI),
+                                      daemon->registry.uri.spa_node,
                                       &iface)) < 0) {
       g_error ("can't get interface %d", res);
       return res;