First cut at support for Retina displays

This is a first cut at supporting Retina displays. Very much a work in progress, but I don't think it breaks anything. There are some changes needed to support this code which would be good to get in place now.

Retina support is provided by a new Java 1.8 dependent LAF. It is experimental and must be explicitly requested; see the Ant task 1.8x. My approach is to start with the Aqua look and feel (which already supports Retina displays) and add features one at a time. Currently, the only additions are the file chooser, the color chooser, and the new Yosemite system font. I chose this approach because the Quaqua painting extensions are not compatible with Retina displays and I don't think it is worth the effort to convert them. Using native Aqua painting is pretty decent in 1.8.