Excluded Sites/Clients Permissions Manager

[screwlooseit]

Is your feature request related to a problem? Please describe.
I would love to have an excluded sites and clients feature present in the permissions manager. This would mean that the permission set could see everything except for a site or client. This would mean you wouldn't have to manually add every client to the permission set leaving out the ones you don't want them to see. It becomes a real hassle when you are managing a multitude of clients that are expanding.

Describe the solution you'd like
An exclude feature for the permissions manager similar to the one that is already set in the automation manager

Describe alternatives you've considered
Manually adding each site by site for allowed perms and adding new clients to the list as you go.

Screenshots included on the areas I've addressed