ISPN-3478 Polish CS API revamp

* use consistent naming
ISPN-3478 Polish CS API revamp

* aligned ClusterLoader and CLusterLoaderConfiguration names (both are loaders)
ISPN-3478 Polish CS API revamp

* add a connection pool to handle parallel entry processing
* add tests to verify parallel entry processing for the existing stores
ISPN-3478 Polish CS API revamp

* use the name "Store" vs CacheStore consistently
ISPN-3478 Polish CS API revamp

* use an interface for ByteBuffer so that store implementors won't need to depend on implementation
ISPN-3478 Polish CS API revamp

* use an interface for MarshalledEntry so that store implementors won't need to depend on the implementation
ISPN-3478 Polish CS API revamp

* MarshalledEntryImpl is a parametriezed type now
ISPN-3478 Polish CS API revamp

*  inline persistence parent pom with the directory name
ISPN-3478 Polish CS API revamp

*  removed unused class DataManipulationHelper
ISPN-3478 Polish CS API revamp

* updated after review