Mapreduce aggregations (Part 1)

This is the complete basic package for aggregations on maps and multimaps. Supplier is not yet fully covered with unittests but those will be added later.
https://hazelcast-l337.sonar.cloudbees.com/drilldown/measures/com.hazelcast:hazelcast-root?metric=coverage&rids%5B%5D=2&rids%5B%5D=3163

com.hazelcast.mapreduce.aggregation.impl,   this package has high test coverage.
however, this class and 3 other, looks like they slipped through with a 0%