Let graphie axes be not-in-the-center

Summary:
Set up graphie to do something reasonable when (0,0) isn't contained
in the graph, and put the axes actually within the axes.

Test Plan:
Edit graphing_points.html and change the range from [[-1, 11], [-1,
11]] to [[2, 11], [2, 11]]. Open /exercises/graphing_points.html, and note that
the axes, tick marks, and labels are now in reasonable positions.

Reviewers: alpert, eater

Reviewed By: eater

Differential Revision: http://phabricator.khanacademy.org/D2543