Pull-to-refresh on unreads screen and streams/PMs screens

[gnprice]

We often have bugs with the symptom that the app doesn't update its view of what messages the user has gotten. This can be frustrating, but as a user what really makes it frustrating rather than mildly annoying is that there's nothing you can do about it, short of force-closing the app and reopening. This has been a recurring complaint from our most active users for basically as long as the app has existed.

In many apps like Gmail, the presented information (e.g., the emails in your inbox) may update on its own but also the user can force a refresh right now, with a pull-to-refresh gesture -- when scrolled to one end of the list, pull as if to scroll further. The app refreshes the info, and a spinner appears while it does so.

We should borrow the same feature.

Ideally the experience we would like to present would make this unnecessary -- the user would see the app automatically keep itself up to date on all the information it's presenting, and would never need this. In the past we've rejected requests for this feature (#1473; #1611 if I'm correctly interpreting that issue; many discussions in chat), often on these grounds. Empirically we have not lived up to that promise, and we should give the user a reasonable tool to handle that.

This issue is for providing this feature on the screens of the main nav: the unreads screen, and the streams and PMs screens. A second issue will track providing this feature on the message list, which is likely to work differently.

[jainkuniya]

@zulipbot claim

[borisyankov]

I still think that the UX will be extremely confusing and might not result often (if ever) in an actual refresh of data.