Bug 17080: Make C4::Members::AddMember uses Koha::Patron->store

Bug 17080: Make C4::Members::AddMember uses Koha::Patron->store

These calls have been added from commit e196f19 (Bug 12633: Remove SQLHelper
in C4::Members) which added a TODO:
"This patch replaced the calls to SQLHelper to use DBIX::Class.
TODO: Move them to Koha::Borrower."

This is now done by this patch: instead of calling DBIx::Class directly
we use Koha::Patron

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>