Summary: Ref T4589. Allow users to adjust visibility settings on files explicitly. This makes it easier to understand and manage upcoming changes in T4589.
Test Plan: Changed the view policy for a file several times.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T4589
Differential Revision: https://secure.phabricator.com/D10129
