ENH: Add a version for the FreeSurferColorLUT_YYYMMDD.txt so that multiple versions can be available.

The first line of the FreeSurferColorLUT.txt file as provided from the freesurfer binary distributions contains a source code date-time stamp
that can be used to version the files unabiguously.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22250 3bd1e089-480b-0410-8dfb-8563597acbee