new_contents: from django.apps import apps
  from django.core.management.base import NoArgsCommand
  
  
  class Command(NoArgsCommand):
      help = ("One-time migration of a project using `django-model-publisher`"
              " DB fields to ICEKit's 'publishing' equivalents")
  
      def handle_noargs(self, *args, **options):
          UrlNode = apps.get_model('fluent_pages.UrlNode')
          for node in UrlNode.objects.all():
              node.publishing_linked = node.publisher_linked
              node.publishing_is_draft = node.publisher_is_draft
              node.publishing_modified_at = node.publisher_modified_at
              node.publishing_published_at = node.publisher_published_at
              node.save()
  
subject: Add command to migrate legacy publisher projects to publishing, re #5