try to use iteratee with immutable message queue

I wrote a trial version that uses almost the same interface as play websockets (Iteratee, Enumerator)
I preferred to add another controller SockJsService2.scala and added the logic to it directly because it was confusing to me and to get the debugging easier.
It passes now test: XhrPolling.test_transport and I added another test locally
There is still some todos but they can be done
If that works properly, we can move it to the plugin later.
You will find some comments in SockJsService2.scala that illustrates how it works because it may be a little confusing.
If you want to make work as before, you can comment the first POST route in the routing file
have fun :smile_cat: