Move SupplierPart and SupplierPriceBreak to the 'Company' app

- https://docs.djangoproject.com/en/2.2/ref/models/options/#django.db.models.Options.db_table
- https://stackoverflow.com/questions/3519143/django-how-to-specify-a-database-for-a-model
- And others, presumably

InvenTree/part/__init__.py

@@ -5,6 +5,5 @@ It includes models for:
 
 - PartCategory
 - Part
-- SupplierPart
 - BomItem
 """