Disadvantage compensation: Usability improvements

Improvement in assessment tool:

• Column "Extra" should always be available as an optional column, even if the user has not yet started the test

Improvements in User management:

• Overview:
  • Link to course and test course element
  • Add column with ID of course element "Test"
• Dialog to create / edit the disadvantage compensation:
  • Add course ID
  • Add course element reference
  • Display structure path of selected course element below dropdown
  • When editing existing entry: display the already chosen test in the dropdown field