* Introduces a BulkDelete API mixin class
- Allows deletion of multiple items against a single API request
* Bump API version
* Adds BulkDelete mixin to StockItemTestResult API class
* refactor "multi BOM Item delete" to use new approach
* Refactor various attachment API endpoints
* Refactor multi delete for StockItem
* Convert remaining enndpoints over
* Fix for API test code