Server fixes

Various irc-server improvements/fixes:
* Improve login failure error reporting. It now sends a `464 ERR_PASSWDMISMATCH` and a private message with a detailed error.
* Only allows connection to connected networks.
* Fix mode reply never reaching client.
* Fix empty user list after joining a channel, which was happening on some networks.
* Easy server message debugging with `DEBUG_SERVER=true node . run`.