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
@ddboer this is a very interesting idea. that way people could include a file from FOSHttpCache instead of copying stuff into their config, or copy the file and keep things more readable.