WB-846 Change default palette to absolute percentile: While changes for...

WB-846 Change default palette to absolute percentile: While changes for palette initialization were made to PaletteFile::setDefaultPaletteColorMapping, it is never used.  VolumeFile::validateMembers() has been updated so that if a volume's map does not have palette color mapping (and is not a label volume), the default will be use to use the Absolute Percentile and the ROY_BIG-BL palette except for an ANATOMY volume with one map which will use the GRAY_INTERP_POSITIVE palette.