Object detection reference training scripts

It's just a code transfer from the reference. Use this.

Name		Name	Last commit message	Last commit date
Latest commit History 3 Commits
img		img
Object Detection.ipynb		Object Detection.ipynb
README.md		README.md
coco_eval.py		coco_eval.py
coco_utils.py		coco_utils.py
engine.py		engine.py
group_by_aspect_ratio.py		group_by_aspect_ratio.py
presets.py		presets.py
train.py		train.py
transforms.py		transforms.py
utils.py		utils.py

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