This currently assumes the event, that is replied to, is already
fetched. If it isn't, it will render an empty reply. In the future we
should fetch replies before rendering them.

fixes compilation issues with last released lmdb++

This also removes an ugly hack, that was needed before.

It is a bit of a hack, but it works...

No idea, why apply visitor doesn't work with temporaries?

Also lays a bit of groundwork for better reply rendering

Thanks to red_sky for the feedback!

This also makes long messages unreadable, because we don't shorten long
usernames anymore. We may eventually want to do that again, but it is
hard with translations and we probably want to shorten the displayname
more, as before this change the message was only ever as long as the
timestamp, which is usually just 5 characters...