Bug 21374: Fix self registration verification

Bug 21374: Fix self registration verification

Test plan:
0) Do not apply the patch
1) Set PatronSelfRegistration  to Allow
2) Set PatronSelfRegistrationVerifyByEmail to Require
3) Try to create a account using self registration and verify it (use link
    in e-mail or take the url from table mesage_queue ;)
    The verificatin url return ISE - DBIx::Class::Row::store_column(): No
    such column 'timestamp' on Koha::Schema::Result::Borrower
4) Apply the patch
5) Try to acces the verification url again - now it should work

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>