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