Pages as tabs

[edemaine]

New top nav layout that replaces "page i of n" and next/prev page with a tab for each page:

[Yevhenii, Alice, Joe]

• [x] Move undo/redo to left of zoom buttons (or add separator)
• [x] Page tabs are scrollable if necessary
  • [ ] Maybe shorten titles too?
• [ ] Pages can have titles (changable by double clicking)
• [x] Icon to show number of people on that page (maxing out at 3 or so)
• [x] Tooltip listing users on a page
• [ ] Add page adds at the end
• [ ] Re-order pages by dragging
• [ ] Button to archive current page
• [ ] Button to duplicate current page
• [ ] Show archived pages toggle
• [ ] Eventual page hierarchy: Chrome-style tab groups that can be minimized, or Vivaldi-style stacked tabs
• [ ] List of users available from popup button on right, and can jump to their location. Maybe hovering over them shows their view rectangle (#5).

Replaces: #135, #102, maybe #18