http: make RoutingSettings a property of the RequestContext

This is groundwork for upcoming PRs.

/cc @sirthias
Speaking of inconsistencies: We currently have
- `extractExecutionContext`
- `extractLog`
- `extractSettings`
- `extractRequestContext`

vs.

- `unmatchedPath`
- `requestInstance`
- `requestUri`

I tend to favor the simple names (without the extract prefix) for their simplicity, complemented with the general `extract` directive.

> Yes, but these are directives and we can treat them differently.

But should we? Whenever I  stumble over a `withXXX` method I know I just get a copy where the `XXX` gets replaced with the supplied value. Why should this be different for directives (vs. simple case classes)?

So a general rule could be:
-  getters a.k.a. extractors (`Directive1+`) -> simple names
- `copy` alias (`Directive0`) -> `with` prefixed
- other `Directive0`s -> `map` prefixed

You seem to prefer the `extract`/`set` prefixes. 

The main issue here is consistency, whatever naming scheme we agree on. :smile: