Replace exec with hue.js

AKA: the *I have no idea if this works* PR. I was working off the hue-cli source, and think I got it right? But this is straight-up YOLO code until you try it with a real Hue.

All the hue.js code is in `lib/lights.js` and is done via the `register()` and `light()` commands.

There's also new stuff you gotta add in `config.json` - your Hue's IP address, and the light number. I think you have those already? If not, they can be discovered via the hue.js API - just lemme know and I'll tweak it.

Unit tests are available for the new code: just run `npm test`.

Oh yeah, and if you want me to merge this with the image stuff you just did, push your changes and I'll give it a shot!