R1:f7f5a5dd34de

Implement update and history controllers in Phragment

Summary: Depends on D7726. This adds a history controller (for viewing a list of patches associated with a fragment) and an update controller, for creating a new patch of a fragment.

Test Plan: Updated and viewed history of fragments.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4205

Differential Revision: https://secure.phabricator.com/D7727