Add command line argument `--ignore-cameras <camera_id> <camera_id> ...`

Based on @alexandreflusin's work on excluding cameras from 3D triangulation when they're occluded, he's figured out what needs to happen to exclude a camera generally. It would be nice to have a command line argument to specify that some cameras should just be ignored for the entire run, e.g. by running `df3d-cli behData/ --ignore-cameras 0 6` for instance.