This uses the Unicode confusable data together with judging how close
two strings are by using the Levenshtein distance.
Adds the commands `name_ban`, `name_unban` and `name_bans`. Kicks
players who join using a banned name and doesn't allow ingame players to
change their names to the banned ones.
See UTS#39 "Unicode Security Mechanisms":
http://www.unicode.org/reports/tr39/
This means that characters with accents or other things around them are
now considered the confusable with the base character.
Fixes#557. Fixes#575.