Bug 30612: Add accountlines method to Koha::Checkout and Koha::Old::Checkout

Bug 30612: Add accountlines method to Koha::Checkout and Koha::Old::Checkout

It would be very useful to have an accountlines method on checkouts objects. In particular it would make fees related to a checkout available from the checkout objects in overdue notices.

Test Plan:
1) Apply this patch
2) prove t/db_dependent/Koha/Account/Line.t
3) prove t/db_dependent/Koha/Checkouts.t

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>