[IMP] project: select project pricelist based on customer pricelist

Add an invisible field `pricelist_id` to project.project form view, so that when
`partner_id` is changed, `onchange_partner_id` method can also set the
pricelist properly (previously, the pricelist was not set because the
field was not in the view).

addons/project_timesheet/project_timesheet_view.xml

@@ -42,6 +42,10 @@
                     <button class="oe_inline oe_stat_button" name="open_timesheets" type="object" attrs="{'invisible':[('invoice_on_timesheets','=',False)]}"
                         icon="fa-calendar" string="Timesheets"/>
                 </xpath>
+                <xpath expr='//field[@name="partner_id"]' position='after'>
+                    <newline/>
+                    <field name="pricelist_id" invisible="1"/>
+                </xpath>
             </field>
         </record>