If you clicked for no more topics and then the server didn't find any,
we once had code that would say "No more topics" in light gray at the
bottom of the topic list.
The feature appears to have been broken by some detail in the
`self.dom` refactoring. More importantly, it's not clear it's useful
as opposed to clutter.
Since we added the `stream.first_message_id` feature, it's now very
rare for the `more topics` option to appear when there aren't in fact
older topics that could be fetched. In cases where there are not, the
UI is still clear about what's happening -- it shows a loading
indicator and then displays a list of topics that doesn't have
anything new.
So we're removing this feature; we can re-add it without too much
difficulty if user feedback in the future suggests it would be useful
after all.
This avoids a stream having potentially near-infinite height when
opened in a stream with a large number of unread topics; the benefit
is that you can easily access the next stream.
We show an unread count next to "more topics" to make it hard to miss
that there might be more, older topics with unread messages.
With CSS work by Anders Kaseorg.
Fixes#13087.
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>