Integrate Yarp's direct forwarding feature

[RolandGuijt]

Yarp has evolved to a point where there are now features that can be used in favor of some custom code implemented earlier. One of these features is forwarding requests where Yarp's new API may be more favorable than the custom one used now.

There are a number of suggestions in this issue.

It would probably mean major breaking changes so some additional discussion is probably necessary.