Phriction - add viewPolicy and editPolicy back-end data

Summary: Ref T4029. this diff makes the pertinent database changes AND adds the migration script. This is important to get the data backend straightened away before we fully ship T4029. Next diff will expose the edit controls for these policies and whatever else work is needed to get that part done right.

Test Plan: made sure the lone project page on my wiki had a project with restrictive view policy. Post migration verified correct policy applied to this lone project page AND most open policy applied to the others

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T4029

Differential Revision: https://secure.phabricator.com/D10814