SSDM-946: - Introducing IntensityRescaling.IImageToPixelsConverter in order to handle BioFormat Index16ColorModel in ImageUtil.rescale() if highQuality8Bit is set. This improves conversion of 12/16-bit images to 8-bit images for Nikon ND2 files considerable. It is also used when thumbnails are created.
- ImageChannelUtils: User defined image re-scaling is always done on 8-bit images.
- ImageChannelUtils: Many refactorings to make code better readable.
- System tests adapted and modified.

SVN: 32547