chapter 6 stuff - see commit msg details
added auxiliary types info
added refined system and business interfaces
changes compared to the hand-drawn collaboration diagrams:
  changed operation syntax to camelCase
  "user" and "uid" has been replaced with "researcher" and "rid"
  create-operations return the id of the created object. They return null/zero in case of failure.
  all get_..._list()-methods have been replaced with get...Ids()-methods. Additionally, get...Details()- and get...DetailsForMany-methods have been added. Rationale to split up the get...list()-methods: separation of concerns, consistency of interfaces, flexibility
  IGroupMgt.createGroup()-signature has been changed. I assume that the password is generated in the system layer.
  output parameters have been changed to return values/return types
  IGroupMgt.get_participant_list() has been renamed to getMemberIds()
  IAppointmentMgt.add() has been renamed to addResearcherToAppointment()
  all operations returning a bool could indicate success/failure
  maybe a few minor other changes
turned photos head up