Bug 12601: Add a foreign key for aqorders.budget_id

Bug 12601: Add a foreign key for aqorders.budget_id

When creating an order, the fund value is mandatory but the DB structure
does not show this constraint.

The aqorders.budget_id field should be linked to aqbudgets.budget_id.

The updatedatabase.pl (entry 3.01.00.077) commented this constraint,
certainly for a retro compatibility reason.

Actually I found some cases (in production) where aqorders.budget_id is
set to "0". To add this constraint, we should add a temporary fund to
linked orphan orders.

Test plan:
0/ Verify it is not possible to create an order not linked to a fund via
the Koha interface.
1/ Using your SQL CLI (or equivalent), create or update 1+ orders and set
"0" in the budget_id field.
2/ Execute the updatedabase script.
3/ Verify that your order is linked to a new fund (which is linked to a
new budget).
4/ Verify the constraint has correctly been added (show create table
aqorders).

Signed-off-by: Paola Rossi <paola.rossi@cineca.it>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>