Moving to transcoder naming and adding a legacy transcoder.

Change-Id: I80ab5e23cacab5885d2556a9cb639924caa3e7ef
Reviewed-on: http://review.couchbase.org/40496
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>