Feature request: warn if the same profile is active on more than one device

[zcutlip]

I accidentally activated my Mac's wireguard profile on my iPhone. Unsurprisingly, this resulted in both devices having a very slow, unreliable VPN connection. This was my mistake of course, but it took a long time to troubleshoot.

For profiles that are synced via iCloud, It would be nice if the Passepartout client could mark them as active so instances of the client on other devices could indicate this in the UI. It could then warn (or prevent?) if the user attempts to activate an in-use profile on two or more devices.

[keeshux]

Moved to #1675