IRCListener WHOIS command 

The IRCListener returns `Unknown command` when a client sends the `WHOIS` command. Client was `irssi`

Server output:
```
 08/04/17 01:45:34 PM [         IRCServer] Client issued an unknown command WHOIS asdf
```

Client output (`irssi`):
```
13:45 -!- Unknown command
```