BUG: check for color transfer functions first

Procedural color nodes may have color look up tables defined,
check for that node class first and if it has a color transfer
function, use it on the model instead.



git-svn-id: http://svn.slicer.org/Slicer4/trunk@22808 3bd1e089-480b-0410-8dfb-8563597acbee