Select all available bodies when rendering a feed story

Summary:
Fixes T4060. The logic here is:

• When you take several actions at once, we show a single feed story for all of them.
• We choose the "most interesting" title for the feed story. For example, "close task" is more interesting than "add CC".

Currently, the issue with this is:

• "Add comment" is the least interesting title. I think this is correct: all other actions are more interesting than the fact that you added a comment.
• We try to conserve the number of objects we need to load by rendering only the most interesting transaction.

To fix this:

• Stop being so conservative; load all of the transactions and all of their PHIDs.
• Add bodies from any transactions which render bodies. In all cases (I think?) this is a maximum of one comment adding a body.

The end result is a story like this:

epriestley closed T123: the building is on fire.

"Okay guys I put the fire out"

Test Plan: See screenshot.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran, asherkin

Maniphest Tasks: T4060

Differential Revision: https://secure.phabricator.com/D7504