Bugfix in questions' options positions

Remove width and height scales, they are no longer necessary.
Make the course list conditionally cacheable

It will be cached only if the user is a regular student, it won't be
cached for teachers and administrators because of the draft courses.
Check if the course is ready when a user enters the reviews view
Merge branch 'fix-options-positions'
Bugfix in options positions
Redirect not enrolled students to the overview...

...if they try to acccess enrolled only views

Before, it returned a forbidden error, now it redirects the user to the
course overview and shows a message telling the user that he is not
enrolled in the course.