Product sale configuration

• New permission group "Allow change sales price on products".
• In Sales - Configuration, new menu "Product categories sale price", for new object "Product category sale price". This new object have the fields: name, % Discount, fixed amount. From the form of this new object you can navigate to its related products.
• In products new fields:Product category sale price, target cost, manual PSP, last price change date.
• Whenever you change the Target Cost, Extra Cost, Sales Price Category fields in products, the sale price of the product will be calculated as follows: PSP = (target cost) * % discount of the price category + Fixed amount field of the sale price category
• In products 2 new actions to assign category for sale price, and to change manual PsP. In order to do any of these 2 actions, the user must belong to the group created in this module. If a user is not in this group, the fields referenced will be read-only.