[models.transforms] Implement RGB and Grayscale transforms, and hook those into our models (closes #15)

[data.augmentations] Move transforms to augmentations; Implement auto-parellisation for ElasticDeformation (partial affects #5); Reflect changes in all relevant submodules

Update Montgomery dataset

See merge request biosignal/software/ptbench!9

[data.datamodule] Fixes cached dataset model transform application; Improves logging and documentation; Estimate loaded sample sizes and RAM occupance

[data.datamodule] Double-check model_transforms are set before datasets are instantiated; Remove model_transforms from constructor (non-sensical); Improve documentation on model-transforms

[data.montgomery/shenzhen.loader] Simplify loaders, adjust some variable names, comments and add some (commented out) test code to visualize generated images

We decided to handle the resizing of the input at the model level and not at the dataset level anymore. Loaders, docstrings and tests of Shenzhen and Montgomery were updated accordingly to only load data, remove black borders and crop to square shape. [image_utils.RemoveBlackBorders] had to be modified to allow functional utilization

[data.montgomery.loader] Use load_pil() instead of load_pil_baw() since Montgomery images are already in grayscale PNG (not black-and-white!)

rgb protocols are not needed anymore since the rgb transform is applied
depending on the model used.