Coupons management - problems and improvements

[arnisjuraga]

• used coupon must bet added with coupon_id or key, not saved in "totals" table merged into "name" and then extracted.
• coupon must be set as used right after new order is created. Probably, in success.php

$this->model_extension_total_coupon->confirm_NEW($order);

• when order is Cancelled, should we "release" coupon?

t.b.c.