Identify through SASL using the convenient ib3 mixins, and
get rid of a bunch of special-case code in the process.
This helps when dealing with channels set to require identified
users, as otherwise channel joins will race NickServ's processing of
the identify message and some channels will end up not serviced by
the bot (an alternative would be to delay joining channels until the
identify success is confirmed, but the implementation for that looks
like it would be at least as complex).
Note this also effectively drops non-SSL IRC support. Given
passwords are sent over this connection, I don't see it as a loss.
Co-Authored-By: Thierry Carrez <email@example.com>