Add HerringRunner tracked data

[rgov]

For HerringRunner, we have a handful of videos that have been manually tagged. Each fish has a single point on them.

We should export the tagging data in a useful format—JSON would be fine, or match the XML format used by the other data sources—and make it available.

[rgov]

The "ground truth" files tend to be a list of

detection_class mid_x mid_y width height

Since we don't have the bounds of this data, we may have to add it.