Phriction - move "move" business logic to the editor
Summary: Ref T4029. Even more code consolidation and cleanup for the long term benefits!
Test Plan: moved a page successfully. tried to move a page to an existing page and got an error. did the two tab trick to try to move a deleted page and got an error.
Reviewers: chad, epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T4029
Differential Revision: https://secure.phabricator.com/D10812