List of warehouses

When you manage multiple warehouses, you sometimes need to get product quantities in a group of warehouses (for instance in the same country). This is not possible with the products for location relate when you select multiple locations in the location view to give accurate results if you select parent/child locations (see comments here: #12543 (closed)). Defining a new view (and a menu entry) which list the warehouses with a context "with_childs=True" will allow knowing product quantities for selected warehouses.