Improve commit audit status icons

Summary:
Ref T9482. These may need a little more work (feel free to shoot me a counter-diff) but try to:

• Never use only color to distinguish between states (for colorblind, etc users).
• Give the "nothing needs to be done" state a more obvious "okay" icon (instead of a question mark).

Test Plan: Looked at some linked commits in Maniphest, the icons made a bit more sense?

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9482

Differential Revision: https://secure.phabricator.com/D17203