fix: ean - now we display ean8 (and not just ean13)

[monsieurtanuki]

Impacted file:

• edit_product_page.dart

What

• To display ean codes in the "edit product" page, we use a package that needs to know the ean format first.
• So far, we assumed that everything was ean13.
• Now we support ean8 too.
• Of course a list of ean types to support would be helpful, with a method to discriminate between them.

Screenshot

ean8	ean13