[streaming] CoGroupedWindowReduceInvokable refactor

[streaming] Grouped window reduce bugfix
[streaming] Added CoBatchedDataStream and CoWindowDataStream with reduce functionality + CoBatchReduce bugfix

[streaming] RAT & Checkstyle fix
Fix the Javadoc link in DataStream class

Fix the Javadoc link for org.apache.flink.api.common.functions.RichFunction and missing method reference in DataStream class.

Author: Henry Saputra <henry.saputra@gmail.com>

Closes #154 from hsaputra/fix_comments_streaming and squashes the following commits:

127e47a [Henry Saputra] Fix the Javadoc link for org.apache.flink.api.common.functions.RichFunction and missing method reference.
[FLINK-1170] Fix faulty input split localization
Pass hostname to split assigner
Avoid clashes by only using the first component of the fully qualified hostname
[FLINK-1170] address pull request review comments

This closes #158
Prevent RPC service from blocking on exceptions during task cleanup on canceling.
[FLINK-1171] Move Scala API tests to flink-tests project

This closes #159