Add 1/3 chance of point being on an inequality

Summary:
Add 'Show me the correct graphs' button

Add 'Show me the correct graph' button to graphing inequalities 1

Add 'Show me the correct graph' button to graphing inequalities 2

Adapt hints to work with points on the line

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Reviewers: eater

Reviewed By: eater

Differential Revision: http://phabricator.khanacademy.org/D10301