Add ButtonBar icons

Summary: Adds an icon set for icons on button bars.

Test Plan: photoshop

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4394

Differential Revision: https://secure.phabricator.com/D8170

scripts/celerity/generate_sprites.php

@@ -36,6 +36,7 @@ $sheets = array(
   'apps-large' => $generator->buildAppsLargeSheet(),
   'payments' => $generator->buildPaymentsSheet(),
   'tokens' => $generator->buildTokenSheet(),
+  'buttonbar' => $generator->buildButtonBarSheet(),
   'docs' => $generator->buildDocsSheet(),
   'gradient' => $generator->buildGradientSheet(),
   'main-header' => $generator->buildMainHeaderSheet(),