R1:c001781264b4

Allow buttons to just be icons

Summary: Let's buttons just be an icon, no pressure to also have text.

Test Plan: UIExamples, Search, Home, Policy Controls... Probably 99% of them.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D18056