Bug 32155: Fix alignment of course details page

Bug 32155: Fix alignment of course details page

This patch eliminates some unnessesary CSS and converts the course details div into a fieldset.

To test:
1. Create or edit an existing course.
2. Search and add an instructor.
3. Note that the columns are misaligned: the name of the course instructor is shown first, then the label "Instructors" is shown next.
4. Add another three instructors.
5. Note that this pushes the labels for the next few fields to the right.
6. Apply patch
7. Try steps 1-4 again and confirm everthing looks and works correctly.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>