Add zone to informal time format.

This was Ross's suggestion rather than spend a bunch of time with client-side local time. The only other place that shows a time (templates in the search results) also just show the time zone of the result, which is UTC.

This is tested, insofar as it doesn't explode, in an integration test. I'm not sure a time format is really worthy of a specific unit test. Especially since those can be royal pains depending on the machine running them.