R1:8247edff98e8

Modularize Owners package transactions

Summary: Converts Owners package transactions to modular transactions.

Test Plan:
- created a new package
- edited all simple properties from the web ui
- checked that project and user owners were added as reviewers appropriately to new diffs
- inspected the change details for various types of path add / remove / update / reorder changes

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley…