Consider starting a local node server for testing

[jasmussen]

A recent commit moved the svg-sprite to use an externally referenced file, great for caching. However for SVG sandboxing reasons, that means the sprite demo page can only be tested when served from http:// or https://, not from file://.

Can we leverage Node here, so that when you run npm start not only does it build changes when you make them, but it serves results on something like http://127.0.0.1:5000?