kiji-modeling: EXP-400. Update TimeRange to be structured like SchemaSpec/PagingSpec.

issue: https://jira.kiji.org/browse/EXP-400
review: https://review.kiji.org/r/1563
commit: https://github.com/kijiproject/kiji-modeling/commit/2b148c0e6b70a6dff24d709bf67f254144848c0f