GKeyFile parses ini-like config files. So the characters '[', ']',
and '=' cannot be used.
We will replace them with '_' now.
This bug was found when a user wanted to connect to an IPv6 address (user@[ipv6:address]).
One problem could be that we get duplicate account names with they would
use one of those 3 characters. But I consider this very unlikely.
Fix https://github.com/profanity-im/profanity/issues/2103
bfc9eb259c