Add gateway/irc and caps

Use recipient-unavailable when we are not connected to the IRC server

Instead of remote-server-not-found

See #3427

Entirely remove the code for the “preferred_from” nick

Since private messages are now always coming from the server-wide JIDs

Merge remote-tracking branch 'linkmauve/die-gc1.0-die'

Consider the nick change only if it is NOT a join

Fix a type stable-id -> stanza-id, and add a test case to be exhaustive

Announce the urn:xmpp:sid:0 NS in MUC's disco#info

As required by XEP 0359

Should fix #3369

Make sure we keep the stable-id and origin-id nodes when required

See https://xmpp.org/extensions/xep-0359.html

Avoid nick changes when joining a room that was already joined

By an other resource, or anything

fix #3423

Don’t treat presence updates as MUC joins

If the user sends a directed presence to an unjoined MUC without a <x/>
element, send a presence error back instead of attempting to join it
again, as this is almost never what the user wants.

Fixes #3415.

Mark all rooms as non-anonymous

close #3390

XEP-0410: implement server-side optimisation for self-pings

This prevents the ping from round-tripping through IRC and
possibly a random other client of the user. Please see XEP-0410
for the rationale.

Fixes #3385.

Do not change our nick if we send a presence to a non-joined channel

fix #3378

Trivial little syntax changes

Fix a bunch of int to unsigned int conversion warnings

Remove a bunch of useless empty lines

Reject messages from unjoined resources, with an error

fix #3346

Channels’ disco#info includes the number of participants

fix #3311

Merge branch 'v8'

Make the global ad-hoc configure command available in fixed mode

fix #3360