Apply all the clang-tidy modernize-* fixes

Add a None type for the Iid class (when the iid is completely empty)

Fix some compilation warning/errors that appear on FreeBSD

Add the missing & for 3 std::string function arguments

Don’t use ! as the separator for nicknames, use % instead

It’s now easier to use. The distinction between a nick and a channel name is
based on the first character (by default it's '#' and '&'). The user doesn’t
have to worry about which separator to use anymore.

fix #3066

Merge remote-tracking branch 'linkmauve/escaped-iid-support'

Add XEP-0106 support to the bridge

This allows the user to join channels containing forbidden characters
in the local part, like #r&d or #group/project.

Support multiple nick session, except for IQs

ref #2556

Style fix

Move all constructors at the top of classes

Revert "Decode incoming JIDs local part according to xep 0106"

This reverts commit ad0465b32051e224f6a234f3ed36494905e59cbf.

Conflicts:
	louloulibs

Decode incoming JIDs local part according to xep 0106

This let users send message to nicks such as Q@CServe.quakenet.org

fix #3047

Merge branch 'fixed_server'

Do not handle the "%" char in a special way, in the fixed_server mode

Also fix some doc

Add support for a fixed_irc_server configuration

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

Implement a way to add callbacks, waiting for an IRC event to return an iq

Rewrite the whole IID usage

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

ref #2468

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.