Added BlockCacheManagerInterface and its implementation

Related to this issue https://github.com/sonata-project/SonataBlockBundle/issues/159
Exactly the same that this piece of code do - https://github.com/sonata-project/SonataBlockBundle/blob/master/Templating/Helper/BlockHelper.php#L328-L359
But it's extra functionality for render method in Templating/Helper/BlockHelper class, doesn't it?