Add refactored plotter widget (creates bar, line, and picture graphs).

All React-related components have been refactored (props, methods, exported
JSON representation, etc); Graphie-related code remainst mostly unchanged.

Test plan:
Tested questions with various combinations of plotting options on local copy.

Reviewers: alpert, jakesandlund, jack

Reviewed By: jack

Differential Revision: http://phabricator.khanacademy.org/D3714