Improve feed stories with "style", and build basic status update stories.

Summary: Straightfoward iteration on feed.
Test Plan:
https://secure.phabricator.com/file/view/PHID-FILE-d07077119dc834e76618/
Reviewed By: codeblock
Reviewers: jungejason, aran, tuomaspelkonen, codeblock
CC: aran, codeblock, epriestley
Differential Revision: 631