Add "Copy" and "Coverage" columns to unified view

Summary:
These aren't being populated yet; they mostly fix some JS errors with inlines.

For example, the inline hover reticle relies on adjusting its width to account for the "copy" column, and failed when the column did not exist.

Test Plan:

• Hovering inlines in unified now works, mostly.
• Interacted with inlines in side-by-side.

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11985