3d plotting enhancements

[hughesadam87]

Not sure how feasible.

Need 3d/thick polygons:

http://www.phyast.pitt.edu/~zov1/gnuplot/png/wall.png

Colormap in 3d plots should have an axis. Like "cbar axis":

http://www.originlab.com/www/products/images/WaterfallPlot.png

Actually, probably should be that way in 1d plots too.