LibGUI: Make GSocket connection asynchronous.

Now connect() will return immediately. Later on, when the socket is actually
connected, it will call GSocket::on_connected from the event loop. :^)

LibGUI/GHttpJob.h

@@ -16,6 +16,8 @@ public:
     virtual const char* class_name() const override { return "GHttpJob"; }
 
 private:
+    void on_socket_connected();
+
     enum class State {
         InStatus,
         InHeaders,