add switches to set the carve mode of any carver

[simsong]

• [x] Have every scanner set the feature_recorder_def flag carve=true if the scanner is going to use the feature recorder for carving
• [ ] Have usage display additional flags for carving
• [ ] Have the flags read and the feature recorder scanner mode be changed This will allow JPEG carving to be disabled, or just disabled for carving of JPEGs that do not require decoding.