Remove websocket behavior from cowboy handler and add websocket example

When I saw that ```Dynamo.Cowboy.Handler``` was using the cowboy websocket handler behavior I believed the intent was to have it handle websocket connections. If that's not the case anymore we can probably remove it.

I also added an example of using the server ```:dispatch``` config option to interface with a cowboy handler.

Feel free to discard if it's not helpful, cheers.