Implement part and join, both ways

Remove IRC colors from the body when forwarding it to XMPP

Send and receive messages

Also correctly respond to PING with the id, escape some XML content, but not
always

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.