Additional user groups shall have correct perms on videos

[tgloeggl]

• Admins in all their administrated courses
• "Dozentenvertretung"
• "Studierendenansicht"

[tgloeggl]

One could set the LTI course id as STUDIP_{course_id}.

Other idea: remove the namespace STUDIP_, because the benefit is to small for the expense.