[IMP] Decouple the quantity for templates and variants

There are cases where we dot NOT want to simply sum the quantities of all the
variants. For example when dealing with manufacturing capacities, we may have
to chose between variants because we can't make ALL of them with the same
components.

So instead of a simple non-modular implementation, we'll let each module define
his own implementation of how to compute the product template's quantity
available for sale.

Conflicts:
	stock_available/__openerp__.py
	stock_available_immediately/__openerp__.py

stock_available/__openerp__.py

@@ -4,7 +4,7 @@
 
 {
     'name': 'Stock available to promise',
-    'version': '9.0.1.0.0',
+    'version': '9.0.1.0.1',
     "author": "Numérigraphe, Sodexis, Odoo Community Association (OCA)",
     'category': 'Warehouse',
     'depends': ['stock'],

stock_available/models/product_product.py

@@ -21,8 +21,11 @@ class ProductProduct(models.Model):
 
         By default, available to promise = forecasted quantity.
 
-        Must be overridden by another module that actually implement
-        computations."""
+        **Each** sub-module **must** override this method in **both**
+            `product.product` **and** `product.template`, because we can't
+            decide in advance how to compute the template's quantity from the
+            variants.
+        """
         for prod in self:
             prod.immediately_usable_qty = prod.virtual_available
 

stock_available/models/product_template.py

@@ -12,12 +12,17 @@ class ProductTemplate(models.Model):
     @api.multi
     @api.depends('product_variant_ids.immediately_usable_qty')
     def _immediately_usable_qty(self):
-        """Compute the quantity using all the variants"""
+        """No-op implementation of the stock available to promise.
+
+        By default, available to promise = forecasted quantity.
+
+        **Each** sub-module **must** override this method in **both**
+            `product.product` **and** `product.template`, because we can't
+            decide in advance how to compute the template's quantity from the
+            variants.
+        """
         for tmpl in self:
-            tmpl.immediately_usable_qty = sum(
-                v.immediately_usable_qty
-                for v in tmpl.product_variant_ids
-            )
+            tmpl.immediately_usable_qty = tmpl.virtual_available
 
     immediately_usable_qty = fields.Float(
         digits=dp.get_precision('Product Unit of Measure'),