Allow router to return controller output.

Since new generic Router has a functionality of a dispatcher (executing controllers), it's handy to pass controller output further to callee (Application), especially when it's JApplicationWeb. It's easy to to override this method in own JApplication instance, but IMHO this gives a hint how to use new MVC.
as per @eddieajau's comment
Merge pull request #1826 from piotr-cz/patch_JApplicationWebRouter

Allow Web application router to return controller output.