kiji-scoring: SCORE-129. Repackage ScoringServer into a submodule of KijiScoring

issue: https://jira.kiji.org/browse/SCORE-129
review: https://review.kiji.org/r/1291
commit: https://github.com/kijiproject/kiji-scoring/commit/dcc1be9285ab34f77f495a1ed4a073bd4c90f282