Maintenance Mode

MeshDB has a maintenance mode. It prevents all access to the site, UI, and API while active.

To enable it, run `manage.py enable_flag MAINTENANCE_MODE` or POST to the `/maintenance/enable/` route

To disable it, run `manage.py disable_flag MAINTENANCE_MODE` or POST to the `/maintenance/disable/` route

There is also a view in the Admin UI that can enable it, though it will not work for disabling.