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.

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

Pagination could get stuck, if the messages request failed.
Section height seemes to have been calculated to late, which would make
some section overlap the next message in some cases. Fix that by doing
the height calculation manually.