Fix server token assignment of servers in the network

1. the directly linked server, our upstream, always has token "1", and
2. for remote servers in the network, the token and description filds
   were interchanged during registration,

therefore up to now no server could be found by Server::Find() using its
assigned server token.
Correctly assign nicks to their respective host servers

Use the "server token" parameter of NICK commands to find the host server and
correctly assign the nick name to this server.

This allows Anope to correctly free all nick names again when (remote) servers
leave the network, which fixes arbitrary "KILL attacks" when such nick names
reconnect later on.

Initial debugging and patch by DukePyrolator, thanks a lot!
Merge pull request #93 from alexbarton/ngircd-fix-servertoken

ngIRCd protocol module: fix servertoken