Adding ignore zones for UA-DETRAC

[agirbau]

UA-DETRAC dataset does not have all the objects in the frames annotated. They use a so-called "ignore zones" to remove the detections that would correspond to False Positives for corresponding to a non-annotated object. This PR filters both ground truth and detections present in the ignore zones.

[Rachel0x0]

Is it to paint the ignore zones black?

[cheind]

There seems to be some new? packages missing from shapely.geometry import Point. I'm not too keen about adding new external libraries until absolutely necessary. Could you rewrite your code without shapely?