SCHEMA-327. Cell encoders should encode the actual schema of the records being encoded

- Updates cell decoders with adjusted reader/writer schema validation.
  This is still incomplete (see SCHEMA-326).
- Adds a test layout for writer-schema mode.

issue: https://jira.kiji.org/browse/SCHEMA-327
review: https://review.kiji.org/r/295
SCHEMA-337. Create module for tools in KijiSchema

issue: https://jira.kiji.org/browse/SCHEMA-337
review: https://review.kiji.org/r/314
SCHEMA-342. Javadoc for Filters methods are backwards.