Add JSON schema for JSON graph format

* http://tools.ietf.org/html/draft-zyp-json-schema-04
* http://tools.ietf.org/html/draft-fge-json-schema-validation-00

Tested against draggabilly.json from the dataflow-noflo demo.
Merge branch 'igorw:json-schema' of https://github.com/igorw/noflo into json-schema
Added JSON schema validation into `grunt test` toolchain via `chai-json-schema`. Ref #96
Merge pull request #190 from trustmaster/json-schema

Json schema validation in specs