Nsa discovery document supports if-modified-since header.

If-modified-since header was not supported because the pceActor was a def and was created every time a reachability call was done. The latestReachability was always empty....
The pceActor is now created once at startup of the application and the def pceRequester looks up the actor (with deprecated actorFor). Verfied manually that the if-modified-since header is working as intended.
Some tests are still broken though......