Scrollbar with miniatures and bird's-eye view

The scrollbar underneath the main strip shows miniature views of all document groups except for the pinned ones, including the ones that are currently out of view. The miniatures corresponding to document groups that are currently in or out of view on the main strip are highlighted with a yellow or gray border respectively. When hovering the scrollbar with the mouse, or when clicking the icon on the right-hand side of the main strip, a bird's-eye view of all unpinned document groups is shown.