Control over client connections on QModbusServer class

On some applications it is useful to monitor the connections and disconnections from the clients to the Modbus Server. At the moment there is no public access to the sockets connecting or disconnecting to the Modbus Server, it only can be done by accessing the children TCP Socket objects on the TCP Server children objects on the Modbus Server.

It would be very helpful having signals on the QModbusServer class for connecting and disconnecting sockets containing the QTcpSocket object.