TRACKING: Consider alternative date rendering

[neiljp]

Currently we show the full date/time for each message, and in user 'last active' times.

The only case we currently don't show the full detail is with years, where we don't show the current year, adding it for messages from previous years. I suspect this doesn't update in real-time as time switches to the next year, but that's fairly rare.

In contrast, the web app shows dates in various formats:

• messages have just a time, with a header for the date part, which can sometimes be eg. yesterday, and the year if appropriate; this header floats, so this can save space in a long discussion (we don't handle this floating header idea in the same way, so it may not)
• messages have dividers between 'significant' times, indicating previous day and next day; not necessarily consecutive, and for long conversations on the previous day helps avoid the need for the date header being visible
• it doesn't actually show 'last active' times?
• in the recent-topics view (which ZT doesn't currently have an equivalent) the most-recent message time is listed, and it is sorted that way by default, with a relative time (eg. n minutes ago, an hour ago, n hours ago, Yesterday, n days ago)

I believe the web app used to have more instances of relative dates/times, but this is the current state.

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The most implementable initial feature might be to explore extracting the date part of a message into date dividers for above/below. The downside is that this may add extra space requirements.

As per the current label, please discuss this feature in chat.zulip.org first.