Improve shipping method factory
Improve shipping method factory

You can now specify an amount for the flat_rate option.

openfoodfoundation/openfoodnetwork,lin-d-hop/openfoodnetwork,openfoodfoundation/openfoodnetwork,mkllnk/openfoodnetwork,Matt-Yorkley/openfoodnetwork,mkllnk/openfoodnetwork,Matt-Yorkley/openfoodnetwork,lin-d-hop/openfoodnetwork,lin-d-hop/openfoodnetwork,mkllnk/openfoodnetwork,lin-d-hop/openfoodnetwork,mkllnk/openfoodnetwork,openfoodfoundation/openfoodnetwork,Matt-Yorkley/openfoodnetwork,openfoodfoundation/openfoodnetwork,Matt-Yorkley/openfoodnetwork