Add "Visible To" property fields for diffs and revisions

Summary: Ref T603. Show object visibility in the UI. This isn't editable or mutable yet, but will be after T2222.

Test Plan: {F48689} {F48690}

Reviewers: chad, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D6361