Check existing `IPN_USE_MANUFACTURER_PART_NUMBER` parameter on startup

[eeintech]

See #210 (comment)

I then got an error about an missing user setting OPN_USE_MANUFACTURER_PART_NUMBER . So in my existing ~/.config/kintree/user/internal_part_number.yaml I added

IPN_USE_MANUFACTURER_PART_NUMBER: true

and now the app runs.