Added +UNWIND+ to Cypher

UNWIND can be used to transform a collection into individual rows.
Minor changes to UNWIND

o Added more a few more tests for edge cases
o UNWIND now does not remove anything from scope,
  only adds a new identifier for the elements
o Tweaked the documentation
Add UNWIND to shell
Add UNWIND to the browser
Merge pull request #2344 from systay/unwind

Add UNWIND to Cypher