Add internal classes and add type hints + mypy.

tests/test_project/app_unique_together/migrations/0001_initial.py

@@ -1,5 +1,7 @@
 # Generated by Django 2.2 on 2019-07-29 21:21
 
+from __future__ import annotations
+
 from django.db import migrations, models
 
 

tests/test_project/app_unique_together/migrations/0002_auto_20190729_2122.py

@@ -1,5 +1,7 @@
 # Generated by Django 2.2 on 2019-07-29 21:22
 
+from __future__ import annotations
+
 from django.db import migrations
 
 

tests/test_project/app_unique_together/migrations/0003_auto_20190729_2122.py

@@ -1,5 +1,7 @@
 # Generated by Django 2.2 on 2019-07-29 21:22
 
+from __future__ import annotations
+
 from django.db import migrations
 
 

tests/test_project/app_unique_together/models.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from django.db import models