feature_request: add stats on annotations

[FlorianMF]

It would be great if UDT could add a feature allowing to generate some simply stats (histograms etc.) for instance for the classification distribution. This would make the stats already present in the tab 'Labeling' (percent complete, ...) even richer. That way the user does not have to manually generate stats using the csv files.

For imge classification this should be quite easy. I don't know how much sense this makes for other interface types ans how difficult this would be to implement. For NER or Text classification this would certainly be interesting as well. For segmentation task one could consider the bounding box' size or location, the area spanned by the polylines.

This is certainly not a must-have for an annotation tool, but it would be a nice plus for a one-in-all solution