R1:3cb67480e063

Adjust keys for new Differential inline comment table

Summary:
Ref T2222. This sequences //before// D7139 and sorts out keys on the table. In particular:

- There was a fairly silly `draft` key modeled after Pholio; drop it.
- Add a `revisionPHID` key. This is queried mostly-transitionally on the revision view screen.
- Add a `changesetID` key. This is queried by a bunch of interfaces that want more surgical results than `revisionPHID` provides.
- Add an `authorPHID, transactionPHID` key. This is…