As a teacher
I want to be able to highlight a section
so the learners know which section to focus on

Some course formats allow teachers to highlight a section. Some others (as Weekly format) highlight a section based on settings, etc., but do not let the teacher change the highlighted section. So we should delegate the action itself to the course format. 

(forget about the rest of options for now)

Designs: https://www.figma.com/file/OfCvqK069Oz6Fvqq2xcZWI/Create-a-course?node-id=2485%3A37352

Acceptance criteria:

1. User needs permissions to set current section
2. Topics format should offer this option while editing mode. 
3. Weekly format should not offer this option.
4. The highlighted section will be marked in both course index and course main content.
5. For the highlighted section the action will be “Remove highlight”

Technical tasks:

• Add section_setmarker section_removemarker state actions