Fix an issue with `darkconsole.always-on` and logged-out users

Summary:
Fixes T3796. When this got split out into tabs, the data endpoints were accidentally locked down. Open them up again if the setting is on.

Also, when you open/close the console we try to save the preference. Just no-op if you're logged out. Previously, you'd see the requests in DarkConsole since they failed.

Test Plan: Enabled `darkconsole.always-on` and toggled the console on and off as a logged-out user. Disabled the preference and verified it was no longer accessible.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3796

Differential Revision: https://secure.phabricator.com/D6886