The obects.inv file from lightning's documentation is missing a lot of
methods, raising errors when building with sphinx. Problematic methods
have been added to the extras.txt and encoded into extras.inv

The CUDA_VISIBLE_DEVICES environement variable is set if a device is
specified or we raise an error if it has not been set.
Code for accelerator handling has been moved to its own utils script.

Some DensenetRS-specific code has been removed from predictor.py, it
will have to be re-added directly inside the forward of the DensenetRS model.