Add better error checking to 'Add to Dashboard'

Summary: Ref T5307. Adds a better query check query, sets required for the name, adds the correct URI for cancelling.

Test Plan: Test a form without a name, fake a query string, test cancel button.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T5307

Differential Revision: https://secure.phabricator.com/D17520