Add Cutmix

[gosha20777]

Add cutmix generator for beter results.
The cutmix generator can be useful for training models and achieving better results. This will help take existing models to a higher level of quality.

Resources that may be useful:

• https://arxiv.org/abs/1905.04899 - the original article
• https://github.com/clovaai/CutMix-PyTorch - a pytorch implementation
• https://github.com/DevBruce/CutMixImageDataGenerator_For_Keras - keras implenentation (not compartable with retinanet)