Replace Sprite-Icons with FontAwesome

Summary: The removes the sprite sheet 'icons' and replaces it with FontAwesome fonts.

Test Plan:
- Grep for SPRITE_ICONS and replace
- Grep for sprite-icons and replace
- Grep for PhabricatorActionList and choose all new icons
- Grep for Crumbs and fix icons
- Test/Replace PHUIList Icon support
- Test/Replace ObjectList Icon support (foot, epoch, etc)
- Browse as many pages as I could get to
- Remove sprite-icons and move remarkup to own sheet
- Review this diff in Differential

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin, hach-que

Differential Revision: https://secure.phabricator.com/D9052