Create Denoising model

[muschellij2]

There is an error on https://github.com/ANTsX/ANTsRNet/blob/master/R/createDeepDenoiseSuperResolutionModel.R#L90
The first argument of layer_add is the inputs (list of tensors) and the second argument is the batch_size. When piped, this is putting outputs in the inputs slot, then list in the batch size. I'm not sure what you want to do here, so I added a stop because it's not fixed.