This patch adds a new EmailFieldPrecidence systempreference to allow
users to set the precicence in which patron email fields should be used
for communications.
Signed-off-by: Caroline Cyr La Rose <caroline.cyr-la-rose@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>