Remove two sneaky log_debug

Support multi-prefix

See http://ircv3.net/specs/extensions/multi-prefix-3.1.html
ref #3103

Correctly handle the usage of ! as a IRC user mode indicator

Since “!” is also the separator between the nickname and the user hostname,
having “!” as the user mode (e.g. !nick!~some@host.bla) would cause the nick
to be empty. Now we skip it if it is a valid user mode indicator.

Convert received modes into roles and affiliations

Use isupport informations to know the user modes when joining

Also remove the duplicate send_self_join methods, user only send_user_join

Use the logger everywhere

Implement part and join, both ways

Implement the Bridge class to translate between the two protocols

Add all useful classes as well: Jid, Iid, IrcChannel, IrcUser etc to
properly keep the informations about what we receive from the IRC server.

Only handle the MUC join stanza, and send the list of users in the IRC
channel to the XMPP user, and the IRC channel’s topic, for now.