SCHEMA-545. Track users of a Kiji instance

 - HBaseKiji is now pinned to the system version being read at construction time.
 - TableLayoutMonitor renamed to ZooKeeperMonitor.
 - HBaseKiji registers itself as a user of the Kiji instance.

issue: https://jira.kiji.org/browse/SCHEMA-545
review: https://review.kiji.org/r/1040