Integrate pytorch lightning

[remtav]

will let us use:

• Distributed Data Parallel (https://pytorch-lightning.readthedocs.io/en/latest/multi_gpu.html)
• Float 16 (https://pytorch-lightning.readthedocs.io/en/latest/apex.html)
• computing cluster (SLURM) (https://pytorch-lightning.readthedocs.io/en/latest/slurm.html)
• Early stopping (https://pytorch-lightning.readthedocs.io/en/latest/early_stopping.html)
• export to ONNX (https://pytorch-lightning.readthedocs.io/en/latest/production_inference.html) etc.

https://pytorch-lightning.readthedocs.io/en/latest/#common-use-cases

[CharlesAuthier]

The new PR switch to hydra include all the base for lightning, the change left to do is the training process mostly.

[remtav]

Some useful resources: https://pytorch-lightning.readthedocs.io/en/stable/starter/new-project.html https://pytorch-lightning.readthedocs.io/en/latest/notebooks/lightning_examples/cifar10-baseline.html?highlight=ligthning%20module#Lightning-Module