Minor updates to UIExamples

Summary:
Ref T4830.

• If the application policy is public, allow logged-out users to browse examples.
• Use standard elements instead of custom ones.

Test Plan: Browsed UIExamples.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T4830

Differential Revision: https://secure.phabricator.com/D8825