Add setStackable to ObjectItemList and use in Config

Summary:
This adds a new method for rendering the object list as a stackable set of items. Good for certain renderings like Config.

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Test Plan: Review list on iOS, Chrome, FF.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4637

src/applications/config/controller/PhabricatorConfigGroupController.php

@@ -72,6 +72,7 @@ final class PhabricatorConfigGroupController
     $engine->process();
 
     $list = new PhabricatorObjectItemListView();
+    $list->setStackable();
     foreach ($options as $option) {
       $summary = $engine->getOutput($option, 'summary');