Fix cases where Category name is translated and domain breaks


In non-english interfaces the
`domain="[('category_id.name', '=', 'Weight')]"` returns nothing since
`category_id.name == 'Poids'`

There does not seem to be any way to refer to model datas within `arch`
of a view, so `product_uom_categ_kgm_ref` was created to only point at
the ID of `product.product_uom_categ_kgm`

Signed-off-by: Sandy Carter <sandy.carter@savoirfairelinux.com>