Separate command to download images

dan/datasets/__init__.py

dan/datasets/download/__init__.py

dan/datasets/download/exceptions.py

dan/datasets/download/images.py

dan/datasets/download/utils.py

dan/datasets/extract/__init__.py

dan/datasets/extract/arkindex.py

dan/datasets/extract/exceptions.py

dan/datasets/extract/utils.py

docs/get_started/training.md

docs/ref/datasets/download/exceptions.md

docs/ref/datasets/download/images.md

docs/ref/datasets/download/index.md

docs/ref/datasets/download/utils.md

docs/ref/datasets/extract/exceptions.md

docs/usage/datasets/download.md

docs/usage/datasets/extract.md

docs/usage/datasets/index.md

docs/usage/predict/index.md

mkdocs.yml