Fetch chart data via async request and redraw charts when the window is resized

Summary:
Depends on D20439. Ref T13279. Some day, charts will probably need to reload themselves or do a bunch of defer/request-shaping magic when they're on a dashboard with 900 other charts.

Give the controller separate "HTML placeholder" and "actual data" modes, and make the placeholder fetch the data in a separate request.

Then, make the chart redraw if you resize the window instead of staying at whatever size it started as.

Test Plan:

• Loaded a chart, saw it load data asynchronously.
• Resized the window, saw the chart resize.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: yelirekim

Maniphest Tasks: T13279

Differential Revision: https://secure.phabricator.com/D20440