Chapters @adminPanel,Back buttons (for admins/teachers/students) and more

Chapters:

- added to admin panel (NEW)

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Back buttons:

- Added for all pages when needed

- check for user instance (Admin -> adminPanel, Teacher -> teacherPanel, Student -> studentPanel) (FIX)

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Delete Test:

- deleteTest replaced for disableTest in adminPanel and teacherPanel (FIX)

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Header:

- added Forum to header (NEW)

- Home is now popularCourses (FIX)

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Startup:

- popularCourses on website startup (FIX)