Extract count/point data from tasks in Fact engines

Summary:
Depends on D19119. Ref T13083. This is probably still very buggy, but I'm planning to build support tools to make debugging facts easier shortly.

This generates a large number of datapoints, at least, and can render some charts which aren't all completely broken in an obvious way.

Test Plan: Ran bin/fact analyze --all, got some charts with lines that went up and down in the web UI.

Subscribers: yelirekim

Maniphest Tasks: T13083

Differential Revision: https://secure.phabricator.com/D19120