Combo deals (old: Combo offers)

User Story: As a center admin, I want to have the ability to set package deals as combination of 2 or more products with a specific discount.

Acceptance Criteria: Package deals need to be modified so you do not need to create every single combination of all your products. The idea would be to create just the different possible combinations with the price change associated and, as result, ggleap detects when two or more products associated to one Package Deals are into the shopping cart so it applies the specified discount.