Summary:
Ref T13520. Generally, make the table of contents look and more like the paths panel:

  - Show a hierarchy, with compression for single-sibling children.
  - Use the same icons, instead of "M D" and "(img)" stuff.
  - Use EditDistanceMatrix to do a piece-by-piece diff of paths changes.
  - Show path changes within the path list.

I'm not entirely sold on this, but it was complicated to write and I've never heard the term "sunk cost fallacy". I think this is mostly a net improvement, but may need some adjustments and followup.

Test Plan: Viewed various changes in Differential and Diffusion, saw a more usable table of contents.

Maniphest Tasks: T13520

Differential Revision: https://secure.phabricator.com/D21183