Usage of several discounts simultaneously (with the same discount type)

[mariannk]

Usage of several discounts simultaneously (with the same discount type). Store owner will be able to manage this option for each discount ("Cumulative with other vouchers").

We also should introduce some kind of discount priority for discounts. Because final price could be distinct if two discounts are applied to the same product or order total depending on priorit. For example, if one of them have "fixed value" and the other one has "percent" discount specified. For example, (price-$10) x 50% is not the same as (price x 50%)-$10