Add squid component.

It seems the only tool supporting http://tools.ietf.org/html/rfc5861
Drop non defined section usage.
Allow to manipulate HTTP headers.
squid: Add Squid to Apache Frontend (Romain)
squid: Add Squid Recipe from erp5-vifib (Romain C.)
apache-frontend: Temp commit before reverse
apache-frontend: Fix instance.cfg for apache frontend, no squid in recipe
squid: Squid use hardcoded domain
apache-frontend: Remove stunnel from apache frontend recipe
squid: Squid use destination ip instead of domain
apache-frontend: Introduce new architecture for apache frontend
apache-frontend: Stop using apache frontend recipes, no more preconfiguration done by apache_frontend, raw apache config is given by master

apache-frontend: remove unused apache_frontend recipe
apache-frontend: Support ssl certificates in apache frontend
apache-frontend: Add promise on apache frontend, its squid and its apache backend
apache-frontend: Small improvments on profile and templates for apache frontend
apache-frontend: Introducing yakari mode for apache-frontend
apache-frontend: Add logrotate for apaches and squid
apache-frontend: introduce default virtualhost with notfound message, add per slave logging
apache-frontend: Use domain instead of server_name
apache-frontend: Add comment on Yakari