Move subhints and definitions above the scratchpad

Summary:
Moves subhints above the scratchpad, and re-enables the scratchpad
on subhints questions

Test Plan:
 * Visit http://localhost:7000/exercises/square_roots_2.html
 * Make sure subhint shows
 * Make sure the scratchpad is enabled
 * Enable the scratchpad and make sure:
    * subhint is still clickable
    * definition is still activatable

Reviewers: eater

Reviewed By: eater

Subscribers: alpert, jascha

Differential Revision: http://phabricator.khanacademy.org/D9117