30 create visualization2

changed the createVisualization argument: used to require both a rule and a gradient. 

Now either a complete set of gsample, gcolor and gvalue variables need to be filled or the rsample, rcolors and rexprs variables need to be filled.

created 2 new functions as well: createVisualizationGradient and createVisualizationRule to create color rules and color gradients seperately.