Bug 21385: Define the Koha object class for orders

Bug 21385: Define the Koha object class for orders

It fixes the following issue:
t/db_dependent/Acquisition/GetBasketsInfosByBookseller.t .. 1/40 Can't
locate object method "_new_from_dbic" via package "Koha::Aqorder"
(perhaps you forgot to load "Koha::Aqorder"?) at
/home/vagrant/kohaclone/Koha/Object.pm line 230.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit b3dee0daf29c4593aee2781307853845a6cd3735)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>