forked from CGM_Public/pretix_original
* OrderChangeManager: Add support for custom operations * OrderChangeManager: Add callback to AddPosition operation This is also meant as a way to fix #5548 * Refs #5557: Checkstyle fix * Refs #5557: Added tests * Refs #5557: Changes requested in the PR review * Refs #5557: Fix error in previous merge conflict * Refs #5557: PR review