feature_request: Label filtering

[FlorianMF]

I would be interesting, especially for annotation reviews, to filter the annotated samples by classes.

The reviewer could choose which samples he would like to review based on their class label. This would be really interesting when you allow the annotators to choose a 'pass' class (e.g. 'dont_know'). Rather than filtering the csv file and then opening the samples separately (or with a script or whatever) or in UDT knowing its index, the reviewer would instantly have access to these samples and could correct them.