Add 'consumable' field to Part

- Indicates that a part can be used to make other parts
- This is the inverse of 'buildable'
- Add this field to the serializer and edit forms
- Display parameter on part info page
- BOM edit window only requests sub-parts that are marked as 'consumable'
- Also added option to edit 'units' field for part

InvenTree/part/serializers.py

@@ -61,6 +61,7 @@ class PartSerializer(serializers.ModelSerializer):
             'units',
             'trackable',
             'buildable',
+            'consumable',
             'trackable',
             'salable',
         ]