Provide a more informative alternative to 404 on invalid shortened Phurl URL
Summary: When accessing an invalid URL on the short Phurl domain, users should see informative message
Test Plan: Open URL in the previously configured Phurl short domain such as https://www.zz.us and see dialog with message. Open https://www.zz.us/u/123 for a valid U123 Phurl and access destination URL.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D14450