[FIX] purchase: Traceback and bad counter computation

On the product_template, the stat button to indicate the purchased quatity
is buggy in several ways.

1/ The states in the read_group domain have been mistaken with the states
   on the picking (clap, clap)
2/ The read_group is seeking the fields product_id and quantity. Too bad, on
   the model the name is unit_quantity (clap, clap)
3/ The displayed PO lines weren't chosen from a domain. So the computed quantity
   didn't correspond to the displayed lines from the button (small clap, clap)
4/ The action_purchase_line_product_tree linked to the stat button is selecting
   the PO lines where the product is the product id. Too bad, on the PO line
   this is a product.product and on the current object this is a product.template
   (epic clap, clap)

addons/purchase/purchase.py

@@ -971,12 +971,12 @@ class ProductProduct(models.Model):
     @api.multi
     def _purchase_count(self):
         domain = [
-            ('state', 'in', ['confirmed', 'approved', 'done']),
+            ('state', 'in', ['purchase', 'done']),
             ('product_id', 'in', self.mapped('id')),
         ]
         r = {}
-        for group in self.env['purchase.report'].read_group(domain, ['product_id', 'quantity'], ['product_id']):
-            r[group['product_id'][0]] = group['quantity']
+        for group in self.env['purchase.report'].read_group(domain, ['product_id', 'unit_quantity'], ['product_id']):
+            r[group['product_id'][0]] = group['unit_quantity']
         for product in self:
             product.purchase_count = r.get(product.id, 0)
         return True

addons/purchase/purchase_view.xml

@@ -539,7 +539,7 @@
 
         <record model="ir.actions.act_window" id="action_purchase_line_product_tree">
             <field name="context">{}</field>
-            <field name="domain">[('product_id','in',active_ids)]</field>
+            <field name="domain">[('product_id.product_tmpl_id','in',active_ids), ('state', 'in', ['purchase', 'done'])]</field>
             <field name="name">Purchases</field>
             <field name="res_model">purchase.order.line</field>
             <field name="view_id" ref="purchase_order_line_tree"/>