kiji-express: EXP-319. Clean up scaladocs in EntityID and some framework classes.

issue: https://jira.kiji.org/browse/EXP-319
review: https://review.kiji.org/r/1406
commit: https://github.com/kijiproject/kiji-express/commit/6034f9a13e14eb77e9d5b4532755c90df12483d7