Include storyText in feed POST data

Summary: I also changed PhabricatorApplicationTransactionFeedStory and the TokenGivenFeedStory to include only the title/first line of the feed story, which is more convenient (previously, strip_tags gave a multi-line story without even any linebreaks) and more consistent with the other story types.

Test Plan: Added a requestbin URL to feed.http-hooks, commented on a Differential, and saw storyText equal to "alpert added a comment to D2: c." in the POST data it received.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T4630

Differential Revision: https://secure.phabricator.com/D8710