Support SVG patterns as a color scheme

[Fil]

we could select a list of "standard textures" to propose as an ordinal color scheme? e.g. {scheme: "textures"}; Plot would be responsible for adding the necessary and would return the corresponding funciri ("url(#texture1)" etc.)

(follow-up on #362)

cc @awiederkehr

related: #805

[tophtucker]

I love the idea Mike mentioned of built-in Cheysson Color Palettes. One other pattern set I don’t see there would be a monochrome categorical set, like just b&w vertical, horizontal, crossed, dotted, zigzagged. I think at Businessweek we had one of those we used a lot.