Ability to filter confidence for predicted boxes on downloaded images when tagging

[abfleishman]

It would be really great to be able to change the confidence threshold on the fly to be able to display bounding boxes in VoTT that have only high or low confidence.

[yashpande]

This looks very similar to #26, except #26 doesn't mention the low confidence. Did you want a way to have only low confidence predictions instead of either only high confidence or both low and high confidence? The latter two are now possible, but the first is not.