Add some missing rendering code to textual feed stories

Summary: Ref T2852. Token given stories currently try to strip_tags() a PHUIFeedView or similar, which doesn't work. Cast it to a string before stripping. This is super gross but I don't want to clean it up until after ApplicationTransactions so we can really clean up all of Feed.

Test Plan: Ran bin/feed republish <id> on a feed story about giving a token to a revision.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2852

Differential Revision: https://secure.phabricator.com/D6733