[streaming] CoGroupedWindowReduceInvokable refactor

[streaming] Grouped window reduce bugfix
[streaming] Added a TypeWrapper which combines two TypeInformations into a Tuple2 TypeWrapper.
[streaming] Added CoBatchedDataStream and CoWindowDataStream with reduce functionality + CoBatchReduce bugfix

[streaming] RAT & Checkstyle fix
[FLINK-1160] Method added to RecordReaders to allow publishing events to specific inputs