Add dynamic pattern option for test images

[dkozma]

Right now, we need to specify a unique RGB value for images so that they can work for visual testing. I was wondering if we can use GeoPattern, an SVG pattern library that will autogenerate SVG patterns based on the hash of the test resource name. This will be helpful for making sure things are rendering properly in visual tests, and even allow us to test if we want to reference test resources as ingredients in other test resources someday.