Properly send error response on presence stanzas

Return a stanza error whenever the IRCClient for a given server does not exist

Instead of ignoring the stanza, we send back an error of type
remote-server-not-found each time it's possible.

Also avoid having to do if (!irc) return; everytime.

fix #3045

Support raw IRC messages

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

fix #2486

Move non-specific adhoc commands into louloulibs

Only keep some biboumi-specific commands into biboumi_adhoc_commands.hpp/cpp

Remove all the libs that are now in louloulibs