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
for the surrogate-control thing: i guess what they mean is that if you use ESI you can use the proper vary headers and then you probably want to cache the things that vary on cookie and similar things too. imagine the "Hello Jerome" block - its included via ESI on every page. so you actually do want that cached at least for a short bit.