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
Of course, users can already include, e.g., our [ban.vcl](https://github.com/FriendsOfSymfony/FOSHttpCache/blob/master/tests/Functional/Fixtures/varnish-3/ban.vcl) in their Varnish config if they want to. However, I agree that moving our VCL into subroutines will improve re-usability.