Fix error in PhabricatorSetupIssueView

Summary:
- Move `prettyPrintJSON()` and make it static.
- Use it from `PhabricatorSetupIssueView`
- Update other `config/` places that use it to call it from the new class.

This fixes a bug in `PhabricatorSetupIssueView` which showed up if the value
was an array and couldn't be rendered by `phutil_escape_html()`.

Test Plan:
- Rendered some config options.
- Went to /config/issue/config.unknown.phame.skins/ without error.

Reviewers: epriestley, btrahan, chad

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4411

src/applications/config/controller/PhabricatorConfigGroupController.php

@@ -74,7 +74,8 @@ final class PhabricatorConfigGroupController
 
       if (!$option->getHidden()) {
         $current_value = PhabricatorEnv::getEnvConfig($option->getKey());
-        $current_value = $this->prettyPrintJSON($current_value);
+        $current_value = PhabricatorConfigJSON::prettyPrintJSON(
+          $current_value);
         $current_value = phutil_render_tag(
           'div',
           array(