NevowServer : added addInfoString to allow extensions to declare some read-only strings to be displayed in settings. Also renamed addExtension in addSettings for clarity.
<?xml version='1.0' encoding='utf-8'?>
<ModbusServerNode xmlns:xsd="http://www.w3.org/2001/XMLSchema" Local_Port_Number="1502" Local_IP_Address="127.0.0.1"/>