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. :^)

Applications/IRCClient/IRCClient.h

@@ -109,6 +109,8 @@ private:
     void handle(const Message&, const String& verbatim);
     void handle_user_command(const String&);
 
+    void on_socket_connected();
+
     String m_hostname;
     int m_port { 6667 };