[+] BO : on order edition, you can add a discount

[+] BO : on order edition, you can delete a discount
// Adding two new columns in order_cart_rule table: id_order_invoice, value_tax_excl

install-dev/sql/upgrade/1.5.0.2.sql

@@ -288,3 +288,5 @@ ALTER TABLE `PREFIX_product` ADD COLUMN `advanced_stock_management` tinyint(1) d
 DELETE FROM `PREFIX_configuration` WHERE `name` = 'PS_PDF_ENCODING';
 DELETE FROM `PREFIX_configuration` WHERE `name` = 'PS_PDF_FONT';
 
+ALTER TABLE `PREFIX_order_cart_rule` ADD `value_tax_excl` DECIMAL(17, 2) NOT NULL DEFAULT '0.00';
+ALTER TABLE `PREFIX_order_cart_rule` ADD `id_order_invoice` INT NOT NULL DEFAULT '0' AFTER `id_cart_rule`;