kiji-scoring: SCORE-135. Move ScoringServer to its own top level project to avoid circular dependency

issue: https://jira.kiji.org/browse/SCORE-135
review: https://review.kiji.org/r/1386
commit: https://github.com/kijiproject/kiji-scoring/commit/db4b2f0ab42c1c02d93db6b0743531e3e1a6c2f3