Use abstract ModelWithCreatedUpdatedFields for Show model

this adds the fields `created_at`, `created_by`, `updated_at` and `updated_by`

program/models.py

@@ -203,7 +203,7 @@ class HostLink(Link):
     host = models.ForeignKey(Host, on_delete=models.CASCADE, related_name="links")
 
 
-class Show(ModelWithImageFields):
+class Show(ModelWithImageFields, ModelWithCreatedUpdatedFields):
     predecessor = models.ForeignKey(
         "self",
         blank=True,