http: make RoutingSettings a property of the RequestContext

This is groundwork for upcoming PRs.

/cc @sirthias
Yes, but these are directives and we can treat them differently. The `with`-prefixes could also have been used for the ones that now have the `extract`-prefix (and in fact they were in the beginning). For me it's never clear what is meant if I see the `withXXX` directive. This doesn't happen with the active (`set` / `extract`) names.