[FLINK-1074] Fix for NULL input tuples in ProjectJoin
[streaming] CoFlatMap & CoGroupReduce functionality
[streaming] Added database-backed state
[streaming] Memcached, MySQl and SQLite support for state management.
[streaming] Refactored db state connectors and added their license

Conflicts:
	flink-addons/flink-streaming/flink-streaming-connectors/pom.xml
[streaming] Refactored stream components with InputHandler & OutputHandler
[streaming] Minor bug and license header fixes
[streaming] Updated DBStates
[streaming] DataStream merge fix + example clean-up
[streaming] CoRecordReader and iterator added + ConnectedDataStream refactor
[streaming] Examples updated with CoFunctions
[streaming] Added JSONParser and updated Twitter connector
[streaming] WindowJoin Example refactored
[streaming] connectors logging and deploy update
[streaming] reduce operator added to DataStream and ConnectedDataStream + grouped batch and windowReduce operators reworked
[streaming] Moved dependencies to enforce correct policy
[streaming] Mutable and Immutable invoke in CoInvokable
[streaming] Added MockCoInvokable, replaced environments with it in CoFunction tests
[streaming] Tests added for Reduce, GroupReduce and BatchGroupReduce invokables
[streaming] Removed assembly execution on maven package for connectors