R1:148a50e48be1

Convert Differential to new layout

Summary:
First pass at converting Differential, I likely have some buggy-poos but thought I'd toss this up now in case very bad bugs present.

To do:
- Need to put status back on Hovercards
- "Diff Detail" probably needs a better design

Test Plan: Looking at lots of diffs, admittedly I dont have harbormaster, etc, running locally. Checked Diffusion for Table of Content changes on small and large commits.

Reviewers: epriestley

Reviewed By: epriestley

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