Refactor comments app to use mixins for comment functionality; update admin interfaces and add historical model fixes

reviews/mixins.py

@@ -0,0 +1,19 @@
+from django.contrib.contenttypes.models import ContentType
+from django.db.models import QuerySet
+
+class ReviewableMixin:
+    """Mixin for models that can have reviews."""
+
+    def get_reviews(self) -> QuerySet:
+        """Get reviews for this instance."""
+        from reviews.models import Review
+        ct = ContentType.objects.get_for_model(self.__class__)
+        return Review.objects.filter(content_type=ct, object_id=self.pk)
+
+    def add_review(self, review: 'Review') -> None:
+        """Add a review to this instance."""
+        from reviews.models import Review
+        ct = ContentType.objects.get_for_model(self.__class__)
+        review.content_type = ct
+        review.object_id = self.pk
+        review.save()