Simplify sidebar submenus and avoid hidden submenus

[amrbashir]

Our current sidebar has overly nested guides and I think it may be harder to discover theses guides and navigate between them. I think the more nested structures could just be simple headers instead of another submenus, so

link
submenu 
  |_ link
    |_ submenu
      |_ link

would be

link
submenu 
  |_ link
  |_ submenu (as small header) (non-clickable) (always expanded)
  |_ link

or just flatten out