muc-bridge users should never persist

fix build

Entirely remove the code for the “preferred_from” nick

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

Do not mark message to bare JID private/no-copy

Always send direct messages to the user’s bare JID

This has the following advantages:

- Works while all resources are offline (persistent channels)
- Helps with combating duplicate messages when sent to different
  resources, resources going offline, carbon-copying etc. etc.

As a side effect, this also makes the MUC PMs not be MUC PMs and
always be emitted from the server-wide JID of the sending user.

Fixes #3313.

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

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

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

Small trivial readability improvement

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.

Actually fix that correctly instead of the opposite

Remove trailing / of fulljids if IRC host is missing

Properly re-convert \01ACTION into a /me when reflected to the sender

fix #3382

It still needs to be fixed properly by cleaning the way we send the messages
in all direction etc. And this is ugly because, with just one message, we do
a conversion in one direction, and then re-convert in the other
direction. But at least it works and users will be happy, even if I’m not
entirely satisfied with the code.

XEP-0410: set not-in-the-room error condition to not-acceptable

XEP-0410 demands that. This changes the error condition for all
pings to the room, even those which aren’t self-pings, if the
sender is not joined.

The conditions of XEP-0410 were based on observing existing
implementations.

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 send the IRC host directly as real JID of the user

Fixes #3381

Remove an unused function (and a useless debug log)

Trivial little syntax changes

Replace a useless shared_ptr by a unique_ptr

MaxHistoryLength now has some sensible default value if the user set a negative one

Remove a bunch of useless empty lines