Add feed integration to generic transactions

Summary: Publish feed stories, including from Pholio. Actual stories are somewhat garbage but it's all display-time; I'm going to do a pass on feed in general.

Test Plan: {F26832}

Reviewers: btrahan, chad, vrana

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2104

Differential Revision: https://secure.phabricator.com/D4140