Input scaling for images

[cwmeijer]

Implement some solution that scales the image to zero to 1 or zero to 255 depending on the XAI method and model.

[gcroci2]

LIME needs RGB values (see issue #254), while KernelSHAP seems to need 0-1 values ("seems" because I wasn't able to let KernelSHAP work with mnist_model.onnx and zero to 255 input). If there is no match between the input image values scale and what the method expects, the user needs to figure out what to do by him/herself.