Update login icons

Summary: Smaller footprint, flat style, updated logos.

Test Plan: Buttons in UIExamples.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D13622

src/applications/celerity/CeleritySpriteGenerator.php

@@ -125,7 +125,7 @@ final class CeleritySpriteGenerator extends Phobject {
       '2x' => 2,
     );
     $template = id(new PhutilSprite())
-      ->setSourceSize(34, 34);
+      ->setSourceSize(28, 28);
 
     $sprites = array();
     $prefix = 'login_';