Turn DarkConsole settings into real settings

Summary:
Ref T4103. These settings long-predate proper settings and are based on hard-coded user properties. Turn them into real settings.

(I didn't try to migrate the value since they're trivial to restore and only useful to developers.)

Test Plan:

• Toggled console on/off.
• Swapped tabs.
• Reloaded page, everything stayed sticky.

Reviewers: chad

Reviewed By: chad

Subscribers: eadler

Maniphest Tasks: T4103

Differential Revision: https://secure.phabricator.com/D16029