New Feature: max-n detection reporting

[humphd]

A feature we've been discussing is having the ability to report the maximum simultaneous detections seen during the video. For example, if there are 4 trout detected at once at 2:32:02, we'd be interested in having that info reported at the end of the video processing. Probably having the max-n value printed to the console, and also an image with the bounding boxes produced, and a video segment that includes this would be useful.

I'm not sure if we always want to do this, or if it should be something you opt into via a flag.

[humphrem]

It would be good to be able to request the x highest maxN detections (e.g. 5 or 10), since ACTION can't distinguish between species and clips will need to be reviewed to find a species-specific maxN. For example, the single highest maxN returned may have a mix of species and not represent the true highest density of the target species.

This feature should be opt in with a flag.