ISPN-4372 Map/Reduce performance is dependent on cache value size
ISPN-4440 Remove setMaxCollectorSize API from MapReduceTask
ISPN-3981 Enhance grouping API to support group manipulation methods

* First implementation. Added getGroup() and removeGroup() methods
ISPN-4452 DummyInMemoryStore should respect fetch arguments on process method.
Fix test to write from cache 0