Use new Guide layout in Config->Welcome

Summary: Ref T11132, swaps in new UI for welcome page using guide modules

Test Plan: Test instance and non instance guides. Test each setting. Unclear on how to test people / Phacility. Just change the URL link?

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T11132

Differential Revision: https://secure.phabricator.com/D16482