[IMP] product: filter and group by category_id on product.template

Was removed (for unknown reason) during refactoring of product and template (opw 611699)

addons/product/product_view.xml

@@ -15,10 +15,12 @@
                     <filter string="Consumable" name="consumable" icon="terp-accessories-archiver" domain="[('type','=','consu')]" help="Consumable products"/>
                     <separator/>
                     <filter string="Can be Sold" name="filter_to_sell" icon="terp-accessories-archiver-minus" domain="[('sale_ok','=',1)]"/>
+                    <field name="categ_id"/>
                     <field string="Product Variant" name="product_variant_ids" filter_domain="['|', ('product_variant_ids.name','ilike',self), ('product_variant_ids.attribute_value_ids.name','ilike',self)]"/>
                     <field name="company_id"/>
                     <field name="pricelist_id" widget="selection" context="{'pricelist': self}" filter_domain="[]" groups="product.group_sale_pricelist"/> <!-- Keep widget=selection on this field to pass numeric `self` value, which is not the case for regular m2o widgets! -->
                     <group  expand='0' string='Group by...'>
+                       <filter string='Category' domain="[]" context="{'group_by' : 'categ_id'}"/>
                        <filter string='Default Unit of Measure' icon="terp-mrp" domain="[]" context="{'group_by' : 'uom_id'}"/>
                        <filter string='Type' icon="terp-stock_symbol-selection" domain="[]" context="{'group_by' : 'type'}"/>
                     </group>