Add gh-pages demo

[nuest]

We can let GitHub host a demo site using a gh-pages branch. Take a look at the sos-js demo how it can be done: 52North/sos-js#9

[nuest]

I created the basic page based on release 0.1, however, wps-js relies on a proxy this does not work:
http://nuest.github.io/wps-js/

@matthesrieke: can you outline the steps we would need to take to become independent of the proxy? When the WPS supports CORS, then we don't need a proxy.