Will invoke .created_on(period) or .updated_on(period) depending on how it is specified in
          each subclass (A queryset obtained from the Tracked* models will have a created_on and
          updated_on models as shortcuts).
        :param request:
        :param queryset:
        :return: filtered queryset.

def queryset(self, request, queryset):
        """
        Will invoke .created_on(period) or .updated_on(period) depending on how it is specified in
          each subclass (A queryset obtained from the Tracked* models will have a created_on and
          updated_on models as shortcuts).
        :param request:
        :param queryset:
        :return: filtered queryset.
        """

        value = self.value()
        try:
            if not value:
                return queryset
            prefix, period = value.split(':')
            if prefix == 'create':
                return queryset.created_on(period)
            elif prefix == 'update':
                return queryset.updated_on(period)
            elif prefix == 'both':
                return queryset.created_or_updated_on(period)
            else:
                return queryset
        except ValueError:
            return queryset