Allow Conduit console to be browsed by logged-out users

Summary:
Ref T4830. A few methods, like conduit.ping, are callable without authentication, so this even has some use cases. Also:

• Make some Differential stuff a little more consistent.
• Use slightly more modern rendering.
• Deprecate the status-oriented user calls; these will be replaced by Calendar methods.

Test Plan: Browsed console as logged out / logged in users.

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4830

Differential Revision: https://secure.phabricator.com/D8826