typesafe-config support in TaskRunner

This extends https://github.com/addthis/hydra/pull/70 by allowing allow TaskRunner to run both hocon and json configuration instead of relying on a separate job command for the hocon format. Create an API that accepts a configuration body as input, and yields the configuration type as output. We may need to tweak the API over time in order to meet our needs. But having this mechanism in place allows for the job validation and related parsing features we want for all types of jobs.