Thumbnail view for preprocessing

[Ultimate-Storm]

Hannah: as discussed with Omar: it would be helpful to re-incorporate the thumbnails back into the preprocessing. previously, in every folder containing the blocks of a cohort we had a folder with thumbnails so that we could quickly scroll through all images and identify outliers that should not be included due to poor quality or inadequate image content. can we have that automaticaly again?

SWE: We will put this feature into utils repo. As it could be part of quality control and separate from(prior to) the preprocessing pipeline.