Add Map/Reduce and Distributed Task cachewrappers for Infinispan 6
Variable entry size in stress tests
Removed CacheWrapper as the superinterface for features
Refactored Infinispan cache wrapper hieararchy
* All wrappers should from now on keep linear hierarchy according to Infinispan versions (one wrapper per plugin)
* Each feature should be implemented by separate object - wrapper and feature can be enriched separately
* Code from the core wrapper moved to Lifecycle and BasicOperations (these are not features) - wrapper should only hold the caches and orchestrate features
* InfinispanWrapper now can work as multi-cache wrapper as well (see StressTest.useBuckets)