Replace action sprite with FontAwesome

Summary: Replaces the action icons in action headers with FontAwesome

Test Plan:

• grep SPRITE_ACTIONS
• grep sprite-actions
• Replace on UIExamples
• Replace on Workboards
• Replace on Dashboards
• Replace on FeedStories

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9230