Remove an unused function

Add a <item/> node in the presence of a leaving participant

fix #3339

Remove the virtual channel feature altogether

Refactor the channel::self to point at the existing user

This way, the user is always up to date, instead of being a duplicate out of
sync.

fix #3258

Avoid sending PART command for unjoined channels

fix #3205

Fix a use after free in IrcChannel::remove_user

Support multiple nick session, except for IQs

ref #2556

Fix a few issues reported by static analyzers

Upgrade to C++14

Better way to leave the dummy room

[WIP] DummyIrcChannel

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

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.