Implement WEBIRC command

Implement WEBIRC command

The WEBIRC command is used by some Web-to-IRC gateways to set the correct
user name and host name of users instead of their own.

Syntax: WEBIRC <password> <username> <hostname> <ip-address>

The <password> must be set using the new configuration variable "WebircPassword" in the [Global] section of ngircd.conf.

Please note that the <ip-address> is currently not used by ngIRCd (we don't store it in the CLIENT structure, only the resolved hostname).