Use WhiteNoise 3.0's new runserver_nostatic feature

See:
http://whitenoise.evans.io/en/stable/django.html#using-whitenoise-in-development

project_name/settings.py

@@ -34,6 +34,10 @@ INSTALLED_APPS = [
     'django.contrib.contenttypes',
     'django.contrib.sessions',
     'django.contrib.messages',
+    # Disable Django's own staticfiles handling in favour of WhiteNoise, for
+    # greater consistency between gunicorn and `./manage.py runserver`. See:
+    # http://whitenoise.evans.io/en/stable/django.html#using-whitenoise-in-development
+    'whitenoise.runserver_nostatic',
     'django.contrib.staticfiles',
 ]