remove not needed files, reorganize inside dan module

dan/cli.py

dan/datasets/extract/arkindex_utils.py

dan/datasets/extract/extract_from_arkindex.py

dan/datasets/extract/utils.py

dan/datasets/format/bessin.py

dan/datasets/format/synist.py

dan/datasets/utils.py

dan/decoder.py

dan/ocr/train.py

prediction-requirements.txt

requirements.txt

setup.py