add pid management contacting a pid server

- fixed minor things in the epicclient
- some formatting corrected
- change the serialization of the RegistrationRequest to
    return a list of status_descriptions
- change template rendering accordingly
- add pid management
    - contact pid server for registration
    - get a pid from the server and display when
      /registered is accessed (only for single files,
      not for prefixes)
add guideline through the demo