As a user
I want to be able to hide and show the course index
so I can manage course index navigation options

☝️ By default, the course index is always displayed on breakpoints ≳ lg

Prototype: https://www.figma.com/proto/OfCvqK069Oz6Fvqq2xcZWI/Create-a-course?node-id=2115%3A135&scaling=min-zoom&hide-ui=1

Acceptance criteria:

1. Course index could be shown/hidden by the user.
2. We store the last status of course index visibility per user (whatever the course is). That means if a user hides the course index in a course index will keep the same visibility as the last time a course was visited. 
3. Course index is available in view mode for all course main page, activity pages, edit activity pages, but not for course settings page and rest of course pages (such as Participants, Grades, Reports, Question Bank, etc.). 
4. Course index will be on the left side of the main course content for LTR languages, and on the right side for RTL languages.
5. An icon will allow users to open/toggle/show the course index in view mode.