Document icons sprite sheet.

Summary: Adds 32 and 64 px images to represent basic documents.

Test Plan: Differential

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5317

scripts/celerity/generate_sprites.php

@@ -33,8 +33,7 @@ $sheets = array(
   'conpher' => $generator->buildConpherenceSheet(),
   'apps-large' => $generator->buildAppsLargeSheet(),
   'tokens' => $generator->buildTokenSheet(),
-// TODO: @chad: should we actually remove this?
-//  'apps-xlarge' => $generator->buildAppsXLargeSheet(),
+  'docs' => $generator->buildDocsSheet(),
   'gradient' => $generator->buildGradientSheet(),
 );