Improve BomItem editing form
Improve BomItem editing form

- Don't allow duplication of an item already in the BOM
- Remove the parent part from the BOM

SchrodingersGat/InvenTree,SchrodingersGat/InvenTree,inventree/InvenTree,inventree/InvenTree,inventree/InvenTree,inventree/InvenTree,SchrodingersGat/InvenTree,SchrodingersGat/InvenTree