Replace the chart in Maniphest Reports with a chart driven by Facts

Summary:
Depends on D20485. Ref T13279. This removes the ad-hoc charting in Maniphest and replaces it with a Facts-based chart.

(To do this, we build a dashboard panel inline and render it.)

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: yelirekim

Maniphest Tasks: T13279

Differential Revision: https://secure.phabricator.com/D20486