RequestFilter adjustments

Make the API more useful by allowing to override the response in pre-request filter so we can build rate-limiting, caching, 304 responses and so on.

Just return non-true from the pre-request handler, and the framework will try to parse it as a response value. Return SS_HTTPResponse to get that delivered to the user.

Needs some more testing - I've only checked against https://github.com/mateusz/controllerpolicy
Hmm did you misread that? The order is the same everywhere - request, response, session, model. Where is it different?

Shortened res and req for readability - otherwise the line needs to be broken up and the whole function header starts looking huge.