Have text-less dropdown buttons look better

Summary: Using icons and dropdown buttons without text looks a little wonky, this resets the CSS a bit.

Test Plan: Review button with icon and text, just icon, just test, and dropdowns.

Reviewers: epriestley

Reviewed By: epriestley

Spies: Korvin

Differential Revision: https://secure.phabricator.com/D18461