Allow list of font names wherever fonts are described

CSS allows a list of font names (such as "Arial,Verdana,SansSerif" to be specified wherever a font name is needed. The list will be searched, and the first font found will be used. It would be helpful (for cross-platform use, if nothing else) if the same capability would be available for Pivot.

There are only two or three places where this would need to be implemented (FontUtilities, Theme, and TerraTheme come to mind). Maybe a few more...