Initial support for Color Wheels

Color Wheels (GDTF attributes Color1, Color2 and ColorMacro1) are now supported. If CMY/RGB color is used together with a ColorWheel, these colors will be added together. An important handling of GDTF and MVR XML files has been implemented to ensure broader compatibility.

• Handle XML files with null byte at the end
• Add support for Color Wheels (Color1, Color2, and ColorMacro1 GDTF attributes)