R1:ea0db5aa9d57

Clean up dropdown carets

Summary: Adds dropdown carets to buttons more universally that are actually dropdowns.

Test Plan: Differential, Application Search, Diffusion. Mobile and Desktop.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D18292