Give PhrictionContent objects (older versions of wiki pages) legitimate PHIDs
Summary: Ref T13077. Prepares for modern API access to document history using standard "v3" APIs.
Test Plan: Ran migration, verified PHIDs appeared in the database. Created/edited a document, got even more PHIDs in the database.
Maniphest Tasks: T13077
Differential Revision: https://secure.phabricator.com/D19092