Previously, dates were always displayed in the relative, "ago" style,
but these become pretty unwieldy for longer time spans, especially since
the ago library I'm using jumps directly from days to years, so it will
show ones like "200 days ago" that are hard to place.
This adds an "adaptive" date display method and uses it almost
everywhere instead. These will use the "ago" style for shorter periods,
and then switch to showing an absolute date for dates longer ago than
that. The threshold for the switch is currently set to 7 days.
Chad Birch