AttendanceRegister backup structure
---------------------------------------
* attendanceregister (no user info)
    - if (attr)
    - course (not needed)
    - name
    - intro (fa: attendanceregister_intro, no itemid) ???
    - introformat
    - type
    - offlinesessions
    - sessiontimeout
    - dayscertificable
    - offlinecomments
    - mandatoryofflinecomm
    - offlinespecifycourse
    - mandofflspeccourse
    - timemodified
        - completiontotaldurationmins  (new with version 2.4.3)

* sessions    (user info)
    - id (attr)
    - register (not needed)
    - userid (annotation)
    - login
    - logout
    - duration
    - online
    - refcourseshortname (determined from refcourse)
    - comments
        - addedbyuserid (annotation)
