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