JCBC-561: Rename parts from binary to kv (key/value) for more expresiveness.

Change-Id: Ife2323646f054897709cfae00257f02559e60748
Reviewed-on: http://review.couchbase.org/41433
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>