Model changes for [#69959426] Add 'reveal' to prediction questions.

https://www.pivotaltracker.com/story/show/69959426
DRYup the answers delegations.  Most answers delegate to question.
Form changes for [#69959426] Add 'reveal' to prediction questions.

https://www.pivotaltracker.com/story/show/69959426
Move prediction.css to a partial.
Form and runtime changes for 'reveal' to prediction questions.[#69959426]

https://www.pivotaltracker.com/story/show/69959426