Add user role to profile and limit page access accordingly (v1)

• Documentation:
  • Added documentation script Codestructure.md for understanding of Django (backend/frontend/testing) and Project Structure
• Registration:
  • Email is now required for registration and has to be unique across users
  • Users have to select a role (Athletes/Coaches) during registration
  • Users will be added to respective role group after successful registration
• Page Access:
  • Athletes cannot access /myathletes.html (will se alert and be redirected to previous page)
  • Coaches cannot access /mycoach.html (will se alert and be redirected to previous page)
• Testing - Backend:
  • Added test scripts for components (i.e. models, views, etc.) to users app (users/tests)
  • Added junit/coverage reports to Gitlab CI/CD
• Admin:
  • "role" added to user profile details