Session Support

Enables session support in a way that you can specify it whenever you need it

```scala
class SessionController extends Controller with SessionEnabled {

  get("/") { implicit request =>
    session.put("foo", "bar")
    render.plain("wooo").toFuture
  }

  get("/value") { implicit request =>
    render.plain(session.get("foo").getOrElse("nothing")).toFuture
  }
}
```
May be just for test reasons it's fine, but in general this is wrong. This could return "" as a response. you should use flatMap for example to build response