Rework Workboard Cards, split up CSS

Summary: Moves CSS into 3 files, Boards, Panels, Cards. Cleans up Workcards to present more info, hide edit until card hover.

Test Plan:
Lots of photoshop. Verify links to edit still work.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D15137