Bug 9822: Alert on adding an order to a basket if budget s exceeded

Bug 9822: Alert on adding an order to a basket if budget s exceeded

2 DB fields are not used: aqbudgets.encumb and aqbudgets.expend.

This patch uses these fields in order to show a warning message if the
budget selected for an order has exceeded.

Test plan:
- Create a new active fund with at least 1 of both warning fields
  ('Warning at (%)' and 'Warning at (amount)').
- Create a new order for a basket with this new fund and a cost >
  warning amount defined for the fund (or using %).
- Save and check that a warning message appears
- Retry playing with all combinations of warning fields

Signed-off-by: Koha Team Lyon 3 <koha@univ-lyon3.fr>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>