new fallback nameservers (#4113)

* the german privacy foundation has dissolved itself and shut down their
  public nameserver. we are now using the public nameserver by Digitalcourage,
  a german privacy organisation (https://en.wikipedia.org/wiki/Digitalcourage)
* the IP for the server of the swiss privacy foundation has changed
  (http://www.privacyfoundation.ch/de/service/server.html)