Provide a history controller for Releeph branches

Summary: Ref T3663. Same as D6785, but for branches. No writes to this table yet.

Test Plan: Clicked "View History", got a blank but non-broken page.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3663

Differential Revision: https://secure.phabricator.com/D6787