Bring Spree::Variant#active so that we can make it return just variants without includes
Bring Spree::Variant#active so that we can make it return just variants without includes

This makes the variants returned not readonly in rails 4 and thus fixes a spec in Spree::VariantsController#destroy

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