Upgrade to Django 2.2 and modern DRF and py.test (#1246)

* Upgrade django and stuff

* Update to Django 2.2 and recent versions of similar packages

* Provide explicit orderings to all models used in paginated queries

* Resolve naive datetime warnings in test suite

* Deal with deprecation warnings

* Fix sqlparse version

src/tests/base/test_models.py

@@ -1748,10 +1748,11 @@ class CachedFileTestCase(TestCase):
         cf.filename = "testfile.txt"
         cf.save()
         assert default_storage.exists(cf.file.name)
+        n = cf.file.name
         with default_storage.open(cf.file.name, 'r') as f:
             assert f.read().strip() == "file_content"
         cf.delete()
-        assert not default_storage.exists(cf.file.name)
+        assert not default_storage.exists(n)
 
 
 class CheckinListTestCase(TestCase):