Add support for Winsor-Newton colors

[dblock]

There're several Winsor-Newton charts:

http://www.winsornewton.com/resource-centre/colour-charts/

Artists Oil Colour
Winton Oil Colour
Griffin Alkyd Fast Drying Oil Colour
Artisan Water Mixable Oil Colour Artists' Oilbar
Artists Acrylic Colour
Galeria Acrylic Colour
Artists Water Colour
Cotman Water Colour
Designers Gouache
Drawing Inks
Calligraphy Inks

The colors have other information, such as Colour name, Colour code, Permanence Rating, Opacity and the ASTM rating.

[dblock]

There's also a "classic" oil chart, I didn't dig into how it differs from WN. Other oil color producers seem to follow it: http://www.oldholland.com/products/classic-oil-colours/classic-oil-colours-colour-chart/