Move symfony cache component

Fix #170, Replace #177

Depends on https://github.com/FriendsOfSymfony/FOSHttpCache/pull/145

*TODO*
* [ ] Wrap up https://github.com/FriendsOfSymfony/FOSHttpCache/pull/145, tag a version and up the required version in composer.json
* [ ] Documentation (see also #178 but note that things changed since then)
should this be kept private instead for now, until we decide whether it should become an extension point ? If we make it protected already, we need to guarantee BC on it.