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/order/templates/order/order_base.html

@@ -195,7 +195,7 @@ src="{% static 'img/blank_image.png' %}"
             {% if tp == None %}
             <span class='badge bg-warning'>{% trans "Total cost could not be calculated" %}</span>
             {% else %}
-            {{ tp }}
+            {% include "price_data.html" with price=tp %}
             {% endif %}
             {% endwith %}
         </td>

InvenTree/order/templates/order/sales_order_base.html

@@ -193,7 +193,7 @@ src="{% static 'img/blank_image.png' %}"
             {% if tp == None %}
             <span class='badge bg-warning'>{% trans "Total cost could not be calculated" %}</span>
             {% else %}
-            {{ tp }}
+            {% include "price_data.html" with price=tp %}
             {% endif %}
             {% endwith %}
         </td>