Have Badges use getMostOpenPolicy for View

Summary: Fixes T8938. Sets by default for new badges, getMostOpenPolicy. Removes ability to edit viewPolicy.

Test Plan: Create a new badge, see its public, assign it, log out, still able to view it.

Reviewers: btrahan, epriestley

Reviewed By: btrahan

Subscribers: epriestley, Korvin

Maniphest Tasks: T8938

Differential Revision: https://secure.phabricator.com/D13702