Send the play queue ID to the server

The server keeps a play queue per client, identified by the X-Queue-Id
header. The client sends the ID it has for the selected server with every
request and keeps the one in each response, which is new after a reset or a
sync. The IDs are saved per server in the [queues] section of settings.cfg,
so the game goes on with the same queue after a restart.

HttpTransport now passes the response headers on to the client.

tests/fakes/autoload_snapshot.gd

@@ -14,7 +14,8 @@ static func take(autoloads: Array[Node]) -> AutoloadSnapshot:
 		for property: Dictionary in autoload.get_property_list():
 			if property.usage & PROPERTY_USAGE_SCRIPT_VARIABLE:
 				var value: Variant = autoload.get(property.name)
-				values[property.name] = value.duplicate() if value is Array else value
+				values[property.name] = (value.duplicate()
+						if value is Array || value is Dictionary else value)
 		snapshot._values[autoload] = values
 	return snapshot