Improve robustnesss of feed text rendering

Summary:
Couple of minor cleanup things here:

  - Pass handles to ApplicationTransactions when rendering their stories; this happened implicitly before but doesn't now.
  - Add `?text=1` to do ad-hoc rendering of a story in text mode.
  - Make Conduit skip unrenderable stories.
  - Fix/modernize some text in the Commit story.

Test Plan: Rendered text versions of stories via Conduit and `?text=1`.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: zeeg, spicyj, epriestley

Differential Revision: https://secure.phabricator.com/D8793