Earlier, we were appending view all subscribers link using
JQuery.append, which leaves open the possibility for the component to
be appended multiple times if the function calling it gets called
multiple times.
It is better to have the link div in right_sidebar.hbs
and then insert the html when required.
Instead of showing the "None" empty message, just hide the whole section
instead. Notably this uses the total user counts and not the number of users
rendered, so it's possible we'll still show the sections when they're partially
loaded or if they have inactive users (in which case we'd show the "view more"
links).
The exception is the "THIS CHANNEL" section which we always want to show,
since it can be confusing to see other sections without this section
present. More conversation on that here:
https://chat.zulip.org/#narrow/channel/101-design/topic/right.20sidebar.20design.20tweaks/near/2099241
