Rich text for PBC response description/title.

Per [73009056](https://www.pivotaltracker.com/story/show/73009056).  Data is represented on the server side so it only needs to have the rendering changed (via html attribute settings) in a few places.  May need to update `display_name` function attribute, but requests already work like this, so it works as a way of referring to responses.

Edit: Redo of PR 1446 because it was added to the wrong branch.