This commit adds the possibility to chose between pounds and kilograms
to express the weight field on the product. This is done so that
companies that worked internally in pounds do not have to convert their
weights back to kilograms for a consistent computation of the rates in
delivery.
We complete the general settings with the selection of the weight's uom.
Validating the setting will create an ir.config.parameter. A static
method defined on product template will return the chosen UOM.
We display "weight_uom_name" on the form view so that the UOM is not
clickable/editable because we fear user would want to edit the UOM
instead of changing it in the res config.
We move the view definition allowing to fill the product's weight from
stock to product to help the generation of the intrastat report without
installing inventory.