Add internal classes and add type hints + mypy.

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

@@ -1,6 +1,8 @@
 # Generated by Django 1.11.18 on 2019-04-14 14:59
 
 
+from __future__ import annotations
+
 from django.db import migrations, models
 
 

tests/test_project/app_drop_table/migrations/0002_delete_a.py

@@ -1,5 +1,7 @@
 # Generated by Django 2.1.10 on 2019-07-19 09:50
 
+from __future__ import annotations
+
 from django.db import migrations
 
 

tests/test_project/app_drop_table/models.py

@@ -1,4 +1,4 @@
-from django.db import models
+# from django.db import models
 
 # class A(models.Model):
 #    field_a = models.IntegerField()