artiq: add dependency jsonschema Support for resolution of https://github.com/m-labs/artiq/issues/1474 Co-authored-by: Stephan Maka <sm@m-labs.hk> Reviewed-on: #38 Co-Authored-By: Astro <sm@m-labs.hk> Co-Committed-By: Astro <sm@m-labs.hk>