Use isupport informations to know the user modes when joining

Also remove the duplicate send_self_join methods, user only send_user_join

Basic handling of modes, both ways

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.