Update mailman-web to use Python 3 (For rolling releases) (#217)

* Update mailman-web to use Python 3

* Update configuration

* Python 3.6 image.

* Use alpine 3.7

* Use new style middleware

* Use alpine 3.6

* In Python 3, urlparse was renamed to urllib.parse

web/mailman-web/settings.py

@@ -100,7 +100,7 @@ INSTALLED_APPS = (
 )
 
 
-MIDDLEWARE_CLASSES = (
+MIDDLEWARE = (
     'django.contrib.sessions.middleware.SessionMiddleware',
     'django.middleware.common.CommonMiddleware',
     'django.middleware.csrf.CsrfViewMiddleware',