[FIX] product: display default_code on create; always display default_co...

...de on product.product

This fix will not only display `default_code` (and `ean13`) under the desired conditions on `product.template` and `product.product` but will also display `default_code` (and `ean13`) on create which is another part of this bug (Issue #2772) which I do not believe has been addressed yet.

reference commit 92d8f15