Add libffi to all Postorius images. (#320)

* Add libffi to all Postorius images.

* Use Django less than a certain version.

* Fix the version constraint.

* Fix uwsgi configuration by using only processes.

postorius/mailman-web/uwsgi.ini

@@ -3,9 +3,6 @@
 uwsgi-socket = 0.0.0.0:8080
 http-socket = 0.0.0.0:8000
 
-#Enable threading for python
-enable-threads = true
-
 # Move to the directory wher the django files are.
 chdir = /opt/mailman-web
 
@@ -14,8 +11,7 @@ wsgi-file = wsgi.py
 
 # Setup default number of processes and threads per process.
 master = true
-process = 2
-threads = 2
+process = 4
 
 # Drop privielges and don't run as root.
 uid = mailman