BOM Display: Multiple fixes
BOM Display: Multiple fixes

- Previous multi-level BOM display changes had broken the table in editing mode
- Simplify code
- Re-implement edit / delete / validate buttons
- Re-enable checkboxes in edit mode

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