kiji-rest: REST-59. Ensure that POSTing a JSON writer_schema doesn't cause an error.

When POSTing a cell with a JSON writer_schema, ensure that an exception isn't
thrown. Previously the output JSON writer_schema was being escaped but the
expected input was a JSON object causing errors. Also updated the dependencies
of Kiji components to their latest.

Reviewer: lsheng, shashir
commit: https://github.com/kijiproject/kiji-rest/commit/879b258bd03784db76a19441c663edc810020cde