SSDM-2328: The two problems described in the comment of the issue are solved. Many reference images of the system tests had to be changed. Most image changes are to small to be visible except merged images in MicroscopyImageDropboxTest.
IntensityRescaling.rescaleIntensityLevelTo8Bits: Improved algorithm which preserves color hue and satuarion.
ImageUtil: Version of rescale() with a representative color channel.
Hdf5ThumbnailGenerator.generateThumbnailInternally(): Using new ImageUtil.rescale function providing representative channel obtained from already available meta-data.
ImageChannelsUtils.rescaleIfNot8Bit: Parameter channelColorOrNull added. This is used to calculated correct levels (based on a threshold) and to re-scale intensities correctly.

SVN: 34515