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.

server/http_transport.gd

@@ -16,8 +16,9 @@ func _init(owner: Node) -> void:
 
 
 ## Requests [param url] and calls [param on_complete] with
-## [code](response_code: int, body: PackedByteArray)[/code]. Connection errors and
-## timeouts are reported with response code 0. [param headers] are sent as-is; a
+## [code](response_code: int, body: PackedByteArray, headers: PackedStringArray)[/code],
+## the headers as [code]"Name: value"[/code] lines. Connection errors and timeouts are
+## reported with response code 0 and no headers. [param headers] are sent as-is; a
 ## [param body] is sent as JSON.
 func request(
 		url: String,
@@ -33,12 +34,14 @@ func request(
 		func(
 				result: int,
 				response_code: int,
-				_headers: PackedStringArray,
+				response_headers: PackedStringArray,
 				response_body: PackedByteArray,
 		) -> void:
 			http_request.queue_free()
-			on_complete.call(response_code if result == HTTPRequest.RESULT_SUCCESS else 0,
-					response_body)
+			if result != HTTPRequest.RESULT_SUCCESS:
+				on_complete.call(0, response_body, PackedStringArray())
+				return
+			on_complete.call(response_code, response_body, response_headers)
 	)
 	var all_headers: PackedStringArray = headers.duplicate()
 	if method == HTTPClient.METHOD_PUT || !body.is_empty():
@@ -47,4 +50,4 @@ func request(
 	if error != OK:
 		http_request.queue_free()
 		push_error("Could not send request to %s (error %d)" % [url, error])
-		on_complete.call(0, PackedByteArray())
+		on_complete.call(0, PackedByteArray(), PackedStringArray())