Summary:
Added the initial storage structure (DB tables and DAO classes)
for Phrequent.
Test Plan:
Apply the patch and run `bin/storage upgrade`. It should
complete successfully.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T2857
Differential Revision: https://secure.phabricator.com/D5476
