Add LUT / Windowing for medical images

[Corbie-42]

For medical images, there is a common mechanism called windowing (see this explanation). The exact method is defined in the DICOM standard.

The window is often adjusted manually in a viewer by holding down a mouse button and moving the cursor, so left-right adjusts the width and up-down the windowing center. This can be pretty slow in JavaScript, so it would be nice to do this in Wasm.

Would you care to add the windowing function to photon?