R1:724be3930f3f

PHUIButtonBarView

Summary: Adds a handy bar full of tiny buttons. Use only when directed. Ref: T4394

Test Plan: View UI Examples.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8169