Adding the ISO8601 format to the utils.format class.

This will allow django_filters and django_rest_framework to properly filter by iso 8601 formatted date time strings. Currently those two projects pull in the ISO_INPUT_FORMATS dictionary from django.utils.format to determine if a string passed in is formatted as a date time. Currently all ISO8601 dates passed into the rest framework are not correctly filtered. This change addresses that by allowing them to be parsed and filtered correctly.
might as well have a trailing comma here too