[Feature request] Make possible binding between boxes, masks and keypoints

[ternaus]

In some tasks, like:

• instance segmentation
• face detection

There is coupling between different targets, say: bounding box + corresponding mask or bounding box and facial keypoints.

=> right now we may have situation when bounding box removed after crop, because it is smaller than min_area, but keypoints remain, or box removed, but parts of the mask reman.

It would be great to have a way to bind different targets.

Related to #836 #745