Closes #5503: ISO 8601 date in UI and alternative format as tooltip

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.

netbox/templates/generic/object.html

@@ -42,8 +42,8 @@
   <h1 class="title">{% block title %}{{ object }}{% endblock %}</h1>
   <p>
     <small class="text-muted">
-      Created {{ object.created }} &middot;
-      Updated <span title="{{ object.last_updated }}">{{ object.last_updated|timesince }}</span> ago
+      Created {{ object.created|annotated_date }} &middot;
+      Updated <span title="{{ object.last_updated|date:'SHORT_DATETIME_FORMAT' }} ({{ object.last_updated|date:'DATETIME_FORMAT' }})">{{ object.last_updated|timesince }}</span> ago
     </small>
     <span class="label label-default">{{ object|meta:"app_label" }}.{{ object|meta:"model_name" }}:{{ object.pk }}</span>
   </p>