fix #3211

fix #3171

fix #3145

fix #3077

Lets the admin choose a local address to bind each outgoing (IRC) socket.

fix #2695

See https://kiwiirc.com/docs/webirc

fix #3135

When set to true, the realname and username are extracted (by default) from
the user’s JID

fix #3136

ref #3136

fix #2472

Messages received on an IRC server JID are forwarded as raw IRC messages.

fix #2486

fix #3047

Also fix some doc

This option lets the administrator choose a specific IRC server, and only
that server can be used with this biboumi instance.

In this mode, JIDs to use are changed like this:

- #chan%irc.example.com@biboumi.example.com      -> #chan@biboumi.example.com
- user!irc.example.com@biboumi.example.com       -> user!@biboumi.example.com
- #chan%irc.example.com@biboumi.example.com/Nick -> #chan@biboumi.example.com/Nick
- %irc.example.com@biboumi.example.com           -> no equivalent
- irc.example.com@biboumi.example.com            -> no equivalent

IRC users and channels are now distinguished by the separator used in the
IID (% or !).

ref #2468