* Apply the same rounding to in message bubbles and conversation list.
Also make them consistent with Android's relative times. Fixes#682
* Show full timestamps when hovering on relative time
* Compute timestamp update delays more precisely:
Set timestamps to self-update as soon as they are able to change
rather than a fixed time since the last update.
* Refactor for customizable/localizable relative times
* Update timestamp tests
* Log timestamp update intervals to help debug #460
When `millis_since` becomes larger than one week, `delay` becomes
negative and is set to Zero. This causes an infinite loop and therefore
100% CPU usage (single thread).
// FREEBIE
Display format consistent with Android:
* relative time for everything from today
* Day of week + time for within the past 7 days
* Static Month Day time for everything older
Each timestamp will only update as often as needed to stay accurate,
which is once a minute, once an hour, once a week, or never.
// FREEBIE
