R1:ce1dbbec3cb1

Add FontAwesome as a font/icon choice

Summary:
This adds FontAwesome and attempts to make use as icons as consistent as possible. May require additional tweaks once we start using, but in practice this is pretty finished.

- Adds FontAwesome
- Adds additional transforms (rotates, spins)
- Adds additional colors
- Better scopes halflings and fontawesome
- Shares CSS between fonts for consistency

Test Plan:
Tested various browsers back to IE8, mobile.

{F146146}

Reviewers: btrahan, epriestley…