kiji-scoring: SCORE-125. Add option to FreshRequestOptions to disable freshening per request

issue: https://jira.kiji.org/browse/SCORE-125
review: https://review.kiji.org/r/1429
commit: https://github.com/kijiproject/kiji-scoring/commit/7fa887e3fe0ca6af0cc6bf78a787f6f98e6a710d