Make various UX improvements to charts so they're closer to making visual sense

Summary: Ref T13279. Fix some tabular stuff, draw areas better, make the "compose()" API more consistent, unfatal the demo chart, unfatal the project burndown, make the project chart do something roughly physical.

Test Plan: Looked at charts, saw fewer obvious horrors.

Subscribers: yelirekim

Maniphest Tasks: T13279

Differential Revision: https://secure.phabricator.com/D20817