Example for 2.3.x (with Atmoshere 2.0.3)

I have created an example for Scalatra 2.3.x with Atmosphere 2.0.3 support (see https://github.com/adamretter/scalatra-website-examples). The example is based on the 2.2 Atmosphere ChatController example.

In addition I have updated the example to use Bootstrap 3.0. It looks tidier and prettier now :-)