The ClientSideWindowHandler currently 'intercepts' page requests and renders an intermediate html output in any case.
We should extend the ClientConfig to determine if the current request should get handled via the ClientSideWindowHandler.
That way it would be possible for a project to enable the windowId mechanism only for certain userAgents or disable it for download pages like e.g. an iCal download.
One of the scenarios would e.g. be to disable this handling for various crawling bots (They currently only get the intermediate page which always contains the same content).