As a teacher
I want to be able to hide and show a section
so the learners can't see the section are not ready and see the content once is ready

Changes visibility of a whole section. 

• Hiding a section hides all activities into that section. 
• Showing a section recovers ‘previous’ visibility for all activities into that section.

(forget about the rest of options for now)

Prototype: https://www.figma.com/proto/OfCvqK069Oz6Fvqq2xcZWI/Create-a-course?node-id=3285%3A38308&scaling=scale-down

Acceptance criteria:

1. User needs permissions to hide and show sections.
2. Section and activities visibility will be changed in the course index and course main content.

Technical tasks:

• Add section_hide and section_show state actions