[WIP] Initial work on cache invalidsation refactoring

This PR introduces the `SuluHttpCacheBundle`, which extends the functionality of the `FOSHttpCacheBundle` and adds 4 handlers: Handlers do 2 things, they update the `Response` object with any headers required, and they invalidate the cache.

This PR refactors the work by @chirimoya and adds new Tag functionalty.

Example response when tags are used:

````
HTTP/1.1 200 OK
Date: Tue, 16 Dec 2014 17:21:24 GMT
Server: Apache/2.4.10 (Unix) PHP/5.6.2
X-Powered-By: PHP/5.6.2
Cache-Control: max-age=240, public, s-maxage=240
X-Cache-Debug: 1
X-Cache-Tags: structure-4dfd5a3a-822e-4f21-b90e-b2ae93907dc1,structure-685c5542-0051-4ce9-a22e-9c4ca438447d,structure-aff47495-de8a-4b34-bfd3-c65e996959b0
X-Reverse-Proxy-TTL: 2400
X-Debug-Token: f22842
X-Debug-Token-Link: /_profiler/f22842
Content-Type: text/html; charset=UTF-8
````
@wachterjohannes @danrot we should actively adopt Prophecy instead of using the Mock thing. Native prophecy support in PHPUnit will be in the next minor release I think.