Include stock item purchase price in pricing cache (#4292)

* Add setting to control pricing calculation from stock items

* Bug fix for displaying a "null" setting

* Add new fields to PartPricing model

* Add code for calculation of min/max stock item costs

* Update pricing display to use stock item pricing

* Add unit testing for new pricing features

* Automatically update pricing when stock item is created or edited

* Increment API version

* Improvements for price rendering

* Update based on feedback:

- Roll stock item pricing into purchase pricing
- Simplify models
- Update unit tests

InvenTree/common/models.py

@@ -390,9 +390,12 @@ class BaseInvenTreeSetting(models.Model):
 
             if create:
                 # Attempt to create a new settings object
+
+                default_value = cls.get_setting_default(key, **kwargs)
+
                 setting = cls(
                     key=key,
-                    value=cls.get_setting_default(key, **kwargs),
+                    value=default_value,
                     **kwargs
                 )
 
@@ -1173,6 +1176,24 @@ class InvenTreeSetting(BaseInvenTreeSetting):
             'validator': bool,
         },
 
+        'PRICING_USE_STOCK_PRICING': {
+            'name': _('Use Stock Item Pricing'),
+            'description': _('Use pricing from manually entered stock data for pricing calculations'),
+            'default': True,
+            'validator': bool,
+        },
+
+        'PRICING_STOCK_ITEM_AGE_DAYS': {
+            'name': _('Stock Item Pricing Age'),
+            'description': _('Exclude stock items older than this number of days from pricing calculations'),
+            'default': 0,
+            'units': 'days',
+            'validator': [
+                int,
+                MinValueValidator(0),
+            ]
+        },
+
         'PRICING_USE_VARIANT_PRICING': {
             'name': _('Use Variant Pricing'),
             'description': _('Include variant pricing in overall pricing calculations'),