Define a minimum set of supported JobScheduler XML answers

Current Situation

• JobScheduler provides detailed answers to XML commands as stated in
  • http://www.sos-berlin.com/doc/en/scheduler.doc/xml.xml
  • http://www.sos-berlin.com/doc/en/scheduler.doc/xml_commands.xml
• Due to ongoing development we cannot keep this interface stable for the upcoming releases, see Deprecation Announcement with JS-1423

Desired Behavior

• The above mentioned XML reference documentation is updated to state which elements and attributes from XML answers are stable.
• Additional elements and attributes in XML answers can be provided, however, they are not part of a public interface and are subject to change with upcoming releases.

Maintainer Notes

• Commercial license holders who make use of an XSD schema for JobScheduler XML answers as in JS-1129 can request services to receive an updated XSD schema for new releases.