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