Added functionality for controlling the executor to use from an operation
Merge pull request #1403 from pveentjer/improvement/3.x/operationservice-executorcontrol

Added functionality for controlling the executor to use from an operatio...
Adding new hadoop styled API
Added getJobTracker to HazelcastInstance
Added JobTrackerConfig
Added AbstractJob to typesafely configure the mapreduce task
Added Map / MultiMap KeyValueSource implementations
Started reimplementation of operations
Added onKeys / keyPredicate methods
started implementing special ExecutorService for execution of MapReduce tasks
Making NodeEngine available
Added Javadoc for most classes and method
Fixed some JavaDoc issues