[IMP] stock: editable lot list view

Makes the production lot list view multi-editable.
Also, sets the `product_id` field readonly because there is an onchange
on this field in the addon product_expiry. So, it's better the field is
always readonly than editable then become readonly when an another addon
will be installed.

Task #2078163

addons/stock/views/stock_production_lot_views.xml

@@ -50,10 +50,10 @@
         <field name="name">stock.production.lot.tree</field>
         <field name="model">stock.production.lot</field>
         <field name="arch" type="xml">
-            <tree string="Lots/Serial Numbers">
+            <tree string="Lots/Serial Numbers" multi_edit="1">
                 <field name="name"/>
                 <field name="ref" optional="show"/>
-                <field name="product_id"/>
+                <field name="product_id" readonly="1"/>
                 <field name="create_date" optional="show"/>
                 <field name="company_id" groups="base.group_multi_company"/>
             </tree>