Start actually showing the phurl urls to users

Summary: Fixes T10679. Added a 'short url' field to the phurl link page and changed the "view url" button to link to the shortened version

Test Plan: Create a phurl link (or navigate to an existing one) and note that there is now a field for "Short URL". Also verified that the "Visit URL" button in the top right still works as intended

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley, yelirekim

Maniphest Tasks: T10679

Differential Revision: https://secure.phabricator.com/D16473