Policy - introduce parentQuery and pass around policy configuration from parent to child

Summary: Ref T603. Ref D6941.

Test Plan: Clicked around all over - looked good. I plan to re-test D6941 to make sure the executeOne case works now as intended

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D6944