Ref T8989, Add a "Visit URL" link to Phurl items.

Summary: Ref T8989, Add a "Visit URL" link to Phurl items and make it actionable if the URI has a valid protocol.

Test Plan:

• Create a Phurl object with a URI of "google.com".
• "Visit URL" action in action view should be greyed out.
• Edit object to have URI "http://google.com" and save. "Visit URL" link should be available and should redirect to the intended URL.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: chad, Korvin

Maniphest Tasks: T8989

Differential Revision: https://secure.phabricator.com/D14379