Make sections collapsable for Topics and Weekly course formats.

As a student 
I want to collapse sections in the course main content area
So I can focus on the most important section for me

Acceptance criteria:

• All users with access to the course will have the option to collapse/expand sections.

• All sections (section 0 included) could be collapsed.

• This new feature should work for both Topics and Weekly course formats.

• By default all sections are expanded.

Out of scope:

• Sections will be collapsable/expandable one by one. Adding an option to collapse/expand all sections is not part of this issue.
• Saving section collapsed/expanded status per user is not part of this issue.

This improvement will help us to build the course index and synchronize section status with course main content area.