Polish CS API revamp

https://issues.jboss.org/browse/ISPN-3478

The following would also require integration, otherwise won't compile:
- https://github.com/infinispan/infinispan-cachestore-leveldb/pull/6
- https://github.com/infinispan/infinispan-server/pull/149
- https://github.com/infinispan/infinispan-cachestore-rest/pull/5