make nameserver information available on http server, add NameServerConfig

make nameserver information available on http server, add NameServerConfiguration
This (and the other changes to `reef-webserver`) create a tight coupling between the webserver and the name service. We should be careful here, as it means that people who want to use the webserver but not the name service pay a price, at the very least in the size of their JAR files. Why do we create this coupling here?