With this commit all dates in the UI are now consistently displayed.
I changed the long date format as suggested by @xkilian and confirmed by my own
research.
* DATETIME_FORMAT
* Before July 20, 2020 4:52 p.m.
* Now 20th July, 2020 16:52
"20th July, 2020" would be spoken as "the 20th of July, 2020" but the "the" and
"of" are never written.
The only exception is `object_list.html`. I tried it but there it does not
work so easily because the dates are passed to Jinja as SafeString.
