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
this is redundant with https://www.varnish-cache.org/trac/browser/bin/varnishd/builtin.vcl?rev=5c5634dbd9211c4b784268166709a22177d643de#L159