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
Not quite exactly. Default example also checks if `Surrogate-Control` header is present, which doesn't match what we want (ESI)