Implemented HttpRequestHandler abstraction

* Pulled onRequest, routeRequest, filter etc methods out of GlobalSettings, and put them into a HttpRequestHandler abstraction.
* Introduced HttpConfiguration abstraction to abstract out http configuration
* Rewrote Scala documentation on intercepting requests
* Didn't rewrite Java documentation on intercepting requests - felt a bit like yak shaving
That's correct, and not just that, it's only used by developers who want to use the cake pattern.