Ethernet_ArduinoUNO_webserver: Added convinient configuration page

Change internal network IP (and port not supported yet):
http://192.168.0.109:80/config1

Change external network IP:
http://192.168.0.109:80/config2

Change MAC:
http://192.168.0.109:80/config3

where 192.168.0.109 is current IP from eprom and 80 is port.