R1:284d7b6a4696

Minor fixes to maniphest feed/notification

Summary:
Added `renderNotificationView()` abstract function to `PhabricatorFeedStory` base class.
Fixed duplicate line in `PhabricatorFeedStoryManiphest` class.
Fixed spacing/formatting in `ManiphestTransactionEditor`.

Test Plan: No functional changes

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: allenjohnashton, ddfisher, aran, Korvin

Differential Revision: https://secure.phabricator.com/D2698