Label important data on charts

Summary:
Ref T13279. Adds client-side support for rendering function labels on charts, then labels every function as important data.

Works okay on mobile, although I'm not planning to target mobile terribly heavily for v0.

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: yelirekim

Maniphest Tasks: T13279

Differential Revision: https://secure.phabricator.com/D20500