Put an inviting green show answer button in front of people submitting issues

Summary: If we think this is a good idea, I need to make the corresponding change in webapp:javascript/exercise-package/problem-template.handlebars after landing.

Test Plan: In local mode, start to submit an issue, but click the new button instead. All hints are displayed.

Reviewers: alex

Reviewed By: alex

CC: alpert

Differential Revision: http://phabricator.khanacademy.org/D5141