Revert "Make sure that api requires authentication by default"

This reverts commit d24c36b95eb2db5095e09945ecc90f521d7f4f78.
Update inventory after_save

It helps to work some logic with the LineItem because at that point we
would have the record id already. Main motivation here is so that
inventory units wouldn't have a line_item id nil when adding products
via backend to an order (in a product-assembly context)