Since there's noImageSource that can load both.svg and bitmap images, and instead there's a separateSvgImageSource andBitmapImage, we currently only attempt to load SVGs when the URL ends in.svg. We don't have much control over the actual downloading/caching operations of these sources.

One potential solution is to do aHEAD request first to get theContent-Type of the image, but it won't be easy to cache that result.

Another would be to download/cache images ourselves.

Relates to#92