JSON Service Registry now made default

Handles https://github.com/Jasig/cas/issues/797

The pull contains:

- Changes that would allow the CAS server webapp and the management webapp to use the JSON Service Registry as the default registry
- The location of the service files can be controlled via properties for both apps
- I included some sample files to show some common ops/settings that can be done with the registry

In the process, I also removed incorrect javadocs and added a default private ctor to fix an issue with serialization.