SCHEMA-335. FormattedEntityId does not support a null salt.

Also fixes SCHEMA-489 (NPE in KijiTableLayout if RowKeyFormat2.salt is null).
SCHEMA-436. Table layout updates must push notifications to ZooKeeper

 - Introduce HBaseTableLayoutUpdater that should eventually handle all
   of the table layout updating process.
 - Minimally plug the layout updater into HBaseKiji.modifyTableLayout()
 - Adds an integration that validates HBaseKiji.modifyTableLayout().

issue: https://jira.kiji.org/browse/SCHEMA-436
review: https://review.kiji.org/r/888
SCHEMA-335. Enable nullable 'salt' field in RowKeyFormat2.

Removing the possibility for this field to be null is a regression;
If the user selects RowKeyEncoding.RAW, this field is ignored and may
be set to null. This is explicitly done by the Kiji shell.