Merge colored images and show them as 1 volume

@lassoan This has been very useful for me to get a very old segmentation from VG Studio Max into Slicer. At the time, I only exported the colored slices (as oppose to exporting them to labelmaps) and I don’t think I have the original data anymore. Two questions:

  1. Is there a different way to manipulate transfer functions for RGBA images (so that I can have better control).
  2. Is there a way for me to import this color stack as a segmentation?