Give the customer the option the choose the quantity in a quotation


I want that the customer can choose the quantity in my quotation.

It's weird that we can not have that option because when you add optional products on a SO, the customer can add a optional product in the quotation and choose them the quantity.

In the picture you see better what i want, the only thing that is not working yet is the action behind the - and + button how can i update this so that the total amount also will change 

this is the code that odoo uses to update the product line if you use optional products.

(together with the js =>sale_management.js)

Thanks for helping me out!