More fixes

- Add a set of template tags for rendering status codes
- Improve build API filtering
- Remove some outdated files
- Fix unit testing

InvenTree/company/templates/company/po_list.html

@@ -1,7 +0,0 @@
-{% for order in orders %}
-<tr>
-    <td>{{ order }}</td>
-    <td>{{ order.description }}</td>
-    <td>{% include "order/order_status.html" with order=order %}</td>
-</tr>
-{% endfor %}