Possibility to easily display images from a lazy-tensor

[sebffischer]

When we define a lazy tensor and preprocess it, there should be a simple way to visualize the resulting tensors as images to check whether the preprocessing is applied correctly and yields sensible results.

torchvision has a function tensor_image_browse.

This should work for both the validation as well as the training data and it should either be interactive or just write the images to disk so they can then be explored.