[IMP] purchase: add Purchases statbutton in procurement form view

In procurement form view display a Purchases stat button that redirects to
the purchase order. It opens the PO form view. Note that Purchase Order field
in Extra Information is left untouched. It is just a shortcut to ease
usability.

addons/purchase/__manifest__.py

@@ -34,6 +34,7 @@ Dashboard / Reports for Purchase Management will include:
         'data/purchase_data.yml',
         'report/purchase_reports.xml',
         'views/purchase_views.xml',
+        'views/procurement_views.xml',
         'views/stock_views.xml',
         'views/res_partner_views.xml',
         'report/purchase_report_views.xml',

addons/purchase/models/purchase.py

@@ -1014,6 +1014,14 @@ class ProcurementOrder(models.Model):
                 self.env['purchase.order.line'].create(vals)
         return res
 
+    @api.multi
+    def open_purchase_order(self):
+        action = self.env.ref('purchase.purchase_order_action_generic')
+        action_dict = action.read()[0]
+        action_dict['res_id'] = self.purchase_id.id
+        action_dict['target'] = 'current'
+        return action_dict
+
 
 class ProductTemplate(models.Model):
     _name = 'product.template'

addons/purchase/views/procurement_views.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<odoo>
+    <data>
+        <record id="procurement_order_view_form_inherit_purchase" model="ir.ui.view">
+            <field name="name">procurement.order.form.inherit.button</field>
+            <field name="model">procurement.order</field>
+            <field name="inherit_id" ref="procurement.procurement_form_view"/>
+            <field name="arch" type="xml">
+                <xpath expr="//button[@name='do_view_procurements']" position="before">
+                    <button name="open_purchase_order" string="Purchases" type="object"
+                            class="oe_stat_button" icon="fa-shopping-cart"
+                            context="{'active_id':purchase_id}"
+                            attrs="{'invisible':[('purchase_id', '=', False)]}">
+                    </button>
+                </xpath>
+            </field>
+        </record>
+    </data>
+</odoo>

addons/purchase/views/purchase_views.xml

@@ -390,6 +390,14 @@
             </field>
         </record>
 
+        <record id="purchase_order_action_generic" model="ir.actions.act_window">
+            <field name="name">Purchase Orders</field>
+            <field name="type">ir.actions.act_window</field>
+            <field name="res_model">purchase.order</field>
+            <field name="domain">[]</field>
+            <field name="view_id" ref="purchase_order_form"/>
+        </record>
+
         <record id="purchase_rfq" model="ir.actions.act_window">
             <field name="name">Requests for Quotation</field>
             <field name="type">ir.actions.act_window</field>