Florian Müllner f3d1c78c7d calendar: Use relative times for notification timestamps
For notifications in the message list, it is usually less relevant
when exactly it occurred, but how long ago. So rather than showing
the exact time and expecting the user to figuring out the timespan
themselves, change the format to something human readable.

https://bugzilla.gnome.org/show_bug.cgi?id=775763
2017-03-01 10:55:21 +01:00
..
2014-01-09 13:23:26 -05:00
2011-11-05 13:05:11 -04:00