Add option to omit patron email from LookupUser

Add option to omit the patron email address in a LookupUserResponse
message.

To omit patron email addresses, specify the following in the config
file:

[behavior]
omit_patron_email = yes

The default is to include patron email addresses in the
LookupUserResponse message.

Signed-off-by: Jeff Godin <jgodin@tadl.org>