Add option to send database id in LookupUser respones message.

Add option to send database id in LookupUser respones message.

Autographics is planning to implement better tracking of users who
change barcodes or have more than one barcode.  To implement this
feature they have asked us to return the user's unique database id
instead of the barcode in the LookupUser response message.  They will
use the database id to track the user on their side, and use the
barcode that the patron entered in all other requests.

Signed-off-by: Jason Stephenson <jason@sigio.com>