Add preferences/configuration settings

* Configuration for Servers/Autojoin
* Server config for `/msg NickServ identify ...` command
* Configuration for Channel font. I would love to use inconsolata, for example, as the channel font. (fixed-width)

(again, really liking the style of this application where it's starting off, makes me wish I had more time to help)

Start by locating the existing server connection, autojoin, NickServ command, and channel rendering or settings entry points. Define how each preference is edited and persisted, including the fixed-width font choice. Done means all three requested settings work consistently across application restarts, with verification of server, channel, and message behavior.

Written by the indexing model from the issue text.