Finalize design of JSON for Datasette 1.0

[simonw]

Tracking issue.

• Redesigned JSON API with ?_extra= parameters #1709
• Implement ?_extra and new API design for TableView #1729
• Figure out design for JSON errors (consider RFC 7807) #1875

[simonw]

Should make sure that every API that returns an object as the top level (that's almost all of them) includes "ok": true to indicate no errors.