Fix emoji in nicknames unleashing zalgo

[Alexander Cobleigh]

cinnamon recently added a cute emoji to their name, but that TOTALLY broke things on my tty.

currently we sanitize all emojis using @fenwick67's fantastic https://github.com/fenwick67/neato-emoji-converter

maybe we should just apply it to nicks? i wonder if mentions will break or-what-have-you.

(i'm also fine with not having emojis in nicknames to simplify things but might be controversial)