Redirect users back to where they added an SSH Key

Summary: Ref T12964. This feels like a cheat, but works well. Just redirect the user back to the form they came from instead of to the key page.

Test Plan: Add a key to a user profile, add a key to an Alamanac device. Grep for PhabricatorAuthSSHKeyTableView and check all locations.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12964

Differential Revision: https://secure.phabricator.com/D18445