Bug 33664: Add ability to cancel order lines in closed baskets

Bug 33664: Add ability to cancel order lines in closed baskets

At the moment it's only possible to cancel order lines while the
basket is still open or from the pending orders page during processing
a shipment. The latter requires you to add a shipment and fake an
invoice. To make things easier we want to optionally allow cancelling
order lines in closed baskets from the basket summary page.

Before applying the patch:

1) Set up data
* Create a new basket
* Create a few order lines, at least 3
* Close the basket
* Receive shipment and receive one order line

2) Verify current behaviour
* On basket summary page: you cannot cancel while the basket is closed
* On the pending orders page you can cancel

Apply patch, run database update, restart_all

3) Verify new behaviour
* Verify that nothing has changed on pending orders and basket summary
* Switch new system preference CancelOrdersInClosedBaskets to "Allow"
* Verify that pending orders hasn't changed a bit
* Verify that you now can cancel your order lines in the closed basket
  Exception: the received order line should not be cancellable

Test anything else that you think might make sense ;)

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>