Classifier training workflow: add step to filter out unwanted annotations

[nathanielrindlaub]

Elena discovered during the training of the MIRAv2 model that the COCO.json exports from Animl can contain annotations that are not part of the filtered class-list. This occurs when a user (either correctly or incorrectly) labeled an image as having two animals of different species, and one of the species was included in the initial filter while the other was not.