Lockdown module: Add an emergency button to lock the site down for all users#66

One feature that we really could be part of your Lockdown section, is an emergency button to lock the site down for all users. Even just for maintenance, it would be extremely useful to be able to lock the site while we are busy, but from a fraud/security point of view, invaluable to stop everything when something serious is going wrong, like theft of digital products by some fraudster for example.