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)
it gives access to the other event dispatcher methods besides adding a subscriber. but as this is all during bootstrap, the user should not do very complicated things hopefully. shall we make it private?