[ADD] Modules sale_cancel_purchase and sale_purchase_link

OpenERP 7.0 Module to cancel a sale order and by the same time, related purchase order lines. That simply delete the lines that are linked to the sale order thanks to sale_purchase_link.

sale_cancel_purchase depends on sale_purchase_link
This modules need sale_cancel_picking that you can find on this PR : https://github.com/OCA/sale-workflow/pull/69 
It works for kits too. There is no outgoing move linked to the sale order or maybe, I don't see what do you mean. But I agree. The "origin" solution is not good.