Hpd image fitting s curve normalisation

Some more improvements to the HPD image fitting.

Add to the returned result object smart pointers to the HPD images used during the fitting.

Also add a new image processing stage, which applies an SCurve filter to remove high intensity areas that can cause the Sobel filter some issues. Better than the previous log(z) approach, as that also affected the low intensity areas and could cause a little bias in the extract radii.