Rescale timeline graphs when zooming into data

Summary:
In some of these graphs, certain timeframes contain large outliers. To
give the viewer a little bit of control in avoiding these outliers,
scaleType:"maximized" allows the timeline to rescale itself to only the
visible data.

Test Plan: ./main.py -d to run the modified templates locally.

Reviewers: marcos

Reviewed By: marcos

Differential Revision: http://phabricator.khanacademy.org/D2110