Merge PR from @chrros95

Several Changes:
- Uwsgi now listens on two sockets 8080 for http protocol and 8000 for uwsgi protocol
- Add a read_timeout in documentation for Nginx configuration 
- Expose 8024 properly in Core image
- Expose 8080 and 8000 both in Web image
- Rearange the commands to get even less number of layers.
- Add SIGINT as stop signal in web because uwsgi needs it shut down gracefully
- Enable threads in default uwsgi configuration

Fix #64, Fix #15

web/mailman-web/uwsgi.ini

@@ -1,6 +1,10 @@
 [uwsgi]
 # Port on which uwsgi will be listening.
-http = :8000
+uwsgi-socket = 0.0.0.0:8000
+http-socket = 0.0.0.0:8080
+
+#Enable threading for python
+enable-threads = true
 
 # Move to the directory wher the django files are.
 chdir = /opt/mailman-web