Minor tweaks to Preferences

Summary:
Get rid of HPHP-only syntax, add a header and width restriction.

Test Plan:
Looked at /preferences/, saved preferences.

Reviewed By: tuomaspelkonen
Reviewers: tuomaspelkonen
CC: tuomaspelkonen
Differential Revision: 92

src/applications/people/storage/preferences/PhabricatorUserPreferences.php

@@ -34,6 +34,6 @@ class PhabricatorUserPreferences extends PhabricatorUserDAO {
   }
 
   public function getPreference($key) {
-    return $this->getPreferences()[$key];
+    return idx($this->getPreferences(), $key);
   }
 }

src/applications/people/storage/preferences/__init__.php

@@ -8,5 +8,7 @@
 
 phutil_require_module('phabricator', 'applications/people/storage/base');
 
+phutil_require_module('phutil', 'utils');
+
 
 phutil_require_source('PhabricatorUserPreferences.php');

src/applications/preferences/controller/edit/PhabricatorEditPreferencesController.php

@@ -87,6 +87,8 @@ EXAMPLE;
           ->setValue('Save Preferences'));
 
     $panel = new AphrontPanelView();
+    $panel->setWidth(AphrontPanelView::WIDTH_WIDE);
+    $panel->setHeader('Phabricator Preferences');
     $panel->appendChild($form);
 
     $error_view = null;