Use sprites for all the menu icons

Summary:
See D3277, D3278.

  - Sprite all the menu icons.
  - Delete the unsprited versions.
  - Notification bolt now uses the same style as everything else.

Test Plan: Looked at page, hovered, clicked things.

Reviewers: btrahan, chad, vrana

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1569

Differential Revision: https://secure.phabricator.com/D3279

scripts/celerity/generate_sprites.php

@@ -61,7 +61,7 @@ $sheet->addCSSHeader(<<<EOCSS
  */
 
 .autosprite {
-  background-image: url(/rsrc/image/autosprite.png);
+  background-image: url(/rsrc/images/autosprite.png);
   background-repeat: no-repeat;
 }
 EOCSS