As a teacher
I want to be able to add a new section between 2 existing sections 
So I don't need to move the sections created at the end of the course to the right position

This issue only applies to Topic format.

Acceptance criteria:

• Teachers could see a new 'Add topic below' option at the end of each topic.
• The new topic will be added below the current topic.
• The changes won't be done client-side. That means the page needs to be reloaded to apply the changes.
• The new section added will be shown also in the course index.

https://www.figma.com/file/OfCvqK069Oz6Fvqq2xcZWI/Create-a-course?node-id=1422%3A2949

UX design: