adjustments to host it on demo.crossbar.io

this PR adds a crossbar config to run the demo locally, plus adjustments to allow us to host the demo on demo.crossbar.io:

- app prefix `io.crossbar.demo.videocontroller`
- dynamic determination of router URL
- hide `run()`behind `__main__`
- correct link to AutobahnJS

The demo implements 2 remoted procedures: `ip()` and `uuid()`. I'm not sure what's the reason for `ip()`. In a hosted environment, this will return a local IP, not necessarily the externally visible IP the browser is connecting to.