added dialog for specifying ip/port of server
the main method can call the SwingConnectDialog with (null, 0) and a dialog will pop up asking port ip and port of the server
or it can call the SwingConnectDialog with a valid ip/port combo (like (127.0.0.1, 5000)), in which case the SwingConnectDialog will check if ip/port is valid and will then start the client. (No dialog will pop up)