EZP-22400: Use FOSHttpCacheBundle

> https://jira.ez.no/browse/EZP-22400
> Depends on https://github.com/ezsystems/ezpublish-kernel/pull/1025

This adds:

* FOSHttpCacheBundle
* Varnish VCL samples

## TODO
* [x] Test with Varnish 3
* [x] Test with Varnish 4
imo PURGE and BAN are two different things. BAN is based on regexp (and the FOSHttpCacheBundle can do more than ban on the path) while PURGE adresses just one URI, but all variants of it.