Policy - move some owners code into an editor class and check policy better
Summary: Ref T7094. We basically need to make sure folks can see repositories before making owners packages about code within. This cleans up things a little bit by moving a bunch of logic out of the storage class and into an editor class.
Test Plan: made a package and it worked! deleted a package and it worked! discovered buggy behavior in more complicated edits and filed T7127; note this bug exists before and after this diff.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T7094
Differential Revision: https://secure.phabricator.com/D11652