kiji-schema: SCHEMA-814. Implement Comparable for KijiRowKeyComponents.

issue: https://jira.kiji.org/browse/SCHEMA-814
review: https://review.kiji.org/r/1914
commit: https://github.com/kijiproject/kiji-schema/commit/bdc097b7f1908dd27a4c86e97d9db9f034290c39