Multisite Support

Hi, could you please add support for multisite installations?

Currently, this plugin only supports locking users per individual sites. I need this capability on the multisite user account master control panel, from where I could lock the user account for ALL sites. It would be super useful.

Basically just implement the existing functionality to the multisite control panel too. There should be hieararchy: if the user is locked on the multisite master control panel, it is locked on all sites. However, if it is locked on only a few sites and not on the master panel, then the lock is not global. Thank you.