Add "most recent" event interval mode in the bucket view

[ErikBjare]

This was the default before I removed it when I introduced the current interval mode, which works fine, if the bucket you're looking at is recently updated. But if not, then you won't see any events in the list nor the timeline.

Makes debugging difficult, because if a watcher dies you want to know when it died. Or if you imported a bucket and you want to know what some of the most recent data looked like.