Add new enumerated type PaletteNormalizationModeEnum that will controls...

Add new enumerated type PaletteNormalizationModeEnum that will controls mapping of data to a normalized range when assigning colors to brainordinates with palette.  It currently has two values, one that normalizes using data in the selected map and another that normalizes using all data in the file containing the selected map.  GUI control has been added to Map Palette Settings widget.  Next step is top implement these normalization modes.