handle message about successful login

[henk84]

WARN -- rfc2812.rb:1393:in `process': Unknown message ":irc-02.netwichtig.ch 900 marvin marvin!marvin@2a01:4f9:2a:f802:0:0:0:50 marvin :You are now logged in as marvin."

rbot should handle that to track whether logging in was successful. I don’t know if it handles the opposite, i.e. a message telling it that logging in failed, which is likely more important to handle.

https://defs.ircdocs.horse/defs/numerics.html#rpl-loggedin-900