novelty output summary

[maitchison]

The classifier should include some summary about the novelty of a track in the JSON output.

It's not clear how to properly summerise the novelty of a track, but here are some ideas

Average.
Max / 90th percentile.
Minimum / 10th percentile.
Novelty at time of highest confidence

These will all tell us slightly different things. My guess is that 10th percentile or novelty at time of highest confidence is the way to go, as we don't really care if the input was novel during unimportant parts of the tracking.

Potentially all 4 could be exported.