TimeUtils: Change daysAgo to calculate difference in calendar days

TimeUtils: Change daysAgo to calculate difference in calendar days

The `daysAgo` method seemed to want to normalize on a calendar day? I
can't really tell what it was trying to do, but the problem is that it
does not take into account any time shift due to time zones so it never
really worked outside of GMT.
So instead a new `calendarDaysAgo` method is added (because I am unsure
on what the `daysAgo` method is trying to do. It can probably be removed).
The new method cleanly calculates difference in calendar days because it
normalizes the two given time stamps on the same time zone.

The `timeAgo` method now used the new method. This fixes #1248.