Maintenance mode

[bkis]

• on/off in admin settings
• init loader stays open unless admin logged in
• all routes blocked unless admin logged in
• /login shows login

[bkis]

This would have to be effective in the API, too. And there is gets a bit tricky: We could add a route dependency for checking if we're in maintenance mode and return something to indicate the route is temporarily unavailable, but it'd (1) still have to be available for admins and (2) would run a check against the current platform state (a little expensive to get) on each request to each endpoint.