Keep history of cost price modification
With #8795 (closed) updating the cost price manually will be lost on the next stock move created.
Indeed we need to store the manual cost price modification in such way that the re-computation can take it into account.
The data to store must be the product, company (and any other cost_price depending fields), the date. It should store an absolute cost_price or a formula to compute new cost_price based on current one (e.g. for 10% reduction: cost_price * 0.9). This data is used by the recompute methods at the end of the day computation and the result is used as new cost_price.
The wizard should be moved in stock module.
The account_stock_continental should be plugged on the recompute cost price update to create automatically (thanks to #7273 (closed)) the accounting move.