* Rewrite AbstractEmailForm render to use cleaned_data
* Add date time formatting to AbstractEmailForm's render method according to Django settings SHORT_DATE_FORMAT and
SHORT_DATETIME_FORMAT
* Previously it was iterating over `form` which left no place to remove
data from the submission without removing the field from the form (which
is inadvisable, as discussed on #4313)
* Preserve order of fields in form emails using cleaned data
* Add a test for consistent date rendering in email forms
* update form customisation examples and add note about date / time formatting in email form usage (docs)
* resolves #3733
* resolves #4313
* adds users view to group view (users filtered by that group)
* adds the ability to go to the users list for the group currently being edited (via header link)
* fix issue where the link to add a new user (when no users found) was broken
* resolves #5801
