[Classification Dataset] Please add WHOI plankton dataset for image classification

Please add WHOI plankton datasets for image classification : the complete dataset (9.1GB, 950k images) and its _small_ subset (1.1GB, 57k images).

API suggestion:
```r
whoi_plankton_dataset()
whoi_small_plankton_dataset()
```

Dataset files can be found in https://huggingface.co/nf-whoi