SCHEMA-693.  Move classes from impl to impl.hbase.

This refactoring already happened in the Cassandra branch.  Doing this
on master now to make eventual merge with Cassandra easier.

Some classes / interfaces we did not move yet to impl.hbase because they
get used in fake HBase - we will refactor these later, when we do
modifications to other projects.

review: https://review.kiji.org/r/1759
issue: https://jira.kiji.org/SCHEMA-693