Merge branch 'python3-manage.py' into 'master'

Get manage.py from Django 2.0

See merge request !719

website/manage.py

 #!/usr/bin/env python
-# flake8: noqa
 import os
 import sys
 
-if __name__ == "__main__":
+if __name__ == "__main__":  # pragma: no branch
     os.environ.setdefault("DJANGO_SETTINGS_MODULE", "thaliawebsite.settings")
     try:
         from django.core.management import execute_from_command_line
-    except ImportError:
-        # The above import may fail for some other reason. Ensure that the
-        # issue is really that Django is missing to avoid masking other
-        # exceptions on Python 2.
-        try:
-            import django
-        except ImportError:
-            raise ImportError(
-                "Couldn't import Django. Are you sure it's installed and "
-                "available on your PYTHONPATH environment variable? Did you "
-                "forget to activate a virtual environment?"
-            )
-        raise
+    except ImportError as exc:  # pragma: no cover
+        raise ImportError(
+            "Couldn't import Django. Are you sure it's installed and "
+            "available on your PYTHONPATH environment variable? Did you "
+            "forget to activate a virtual environment?"
+        ) from exc
     execute_from_command_line(sys.argv)