Bug 15531: Add support for standing orders

Bug 15531: Add support for standing orders

This allows creation of special baskets that include standing orders.
These orders do not have a known quantity (and may not have a known
price in advance). Upon receipt, the received items are split into a new
completed order.

Test plan:
  1) Run updatedatabase.pl.
  2) Run prove t/db_dependent/Acquisition/StandingOrders.t . (and the
     other Acquisition tests).
  3) Create a new basket, mark it as a standing order basket.
  4) Add an order to this basket, and notice that the quantity field is
     missing (and thus not required).
  5) Receive items for this order, and notice that the original order is
     unchanged. The new child order line should have the correct price
     and quantity information.

(Note: the QA tools output what seems to be a spurious spelling error
for Test::More's "isnt" in StandingOrders.t.)

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>