Adapt helper functions and some demos to PsychDefaultSetup(2);

Make helper functions adaptive to current WhiteIndex().
Make some demos adaptive, others to use PsychDefaultSetup(1);
Fix some bugs along the way…
All our "regular" demos still assume a 0-255 default color range. They
need to get adapted to 0-1 range, or protected via
PsychDefaultSetup(1); in the long term.