hadoopcompatibility: Wrappers and support for basic mapred hadoop tasks

* wrappers for Mapper, Reducer and Combiner (as a local Reducer)
* interface for Wrappers of OutputCollectors and a default implementation
* New full example of Wordcount using mapred Mapper and Reducer
* Updated test case
hadoopcompatibility: Modified hadoopcompatibility stucture in accordance to #777.
hadoopcompatibility: Implemented Record unwrapping iterator of values to use in reduce function.