Add liststosources management command

This command will be used as part of the backward compatible migration process.
It creates or updates `Source` objects from `FacilityList` objects and also
updates the `source` foreign key on related `FacilityListItems`.

It is intended that this command be removed after deployed application code is
updated to create and reference `Source` objects.

src/django/api/management/commands/liststosources.py

@@ -0,0 +1,42 @@
+from django.core.management.base import (BaseCommand)
+from django.db import transaction
+
+from api.models import FacilityList, FacilityListItem, Source
+
+
+@transaction.atomic
+def list_to_source(facility_list):
+    source_qs = Source.objects.filter(
+        source_type=Source.LIST, facility_list=facility_list)
+    if source_qs.exists():
+        source = source_qs.first()
+    else:
+        source = Source(source_type=Source.LIST,
+                        facility_list=facility_list)
+
+    source.contributor = facility_list.contributor
+    source.is_public = facility_list.is_public
+    source.is_active = facility_list.is_active
+    source.save()
+
+    # Override auto_now values by using a queryset update
+    Source.objects.filter(pk=source.pk).update(
+        created_at=facility_list.created_at,
+        updated_at=facility_list.updated_at)
+
+    FacilityListItem.objects \
+                    .filter(facility_list=facility_list) \
+                    .update(source=source)
+
+
+def lists_to_sources():
+    for facility_list in FacilityList.objects.all():
+        list_to_source(facility_list)
+
+
+class Command(BaseCommand):
+    help = ('Create/update Source records from FacilityList records and '
+            'connect the Source records to FacilityListItem records.')
+
+    def handle(self, *args, **options):
+        lists_to_sources()