implement subscription

XIONControlPanel/Servers/ServerProtocol.swift

@@ -16,9 +16,15 @@ enum ConnectionStatus
     case error
 }
 
-protocol Server
+protocol ServerDelegate: AnyObject
+{
+    func server(_ server: Server, deviceChangedState: AnyDevice)
+}
+
+protocol Server: AnyObject
 {
     var connectionStatus: ConnectionStatus { get }
+    var delegate: ServerDelegate? { get set }
     
     /// Designated initializer. Takes an API endpoint URL
     init(_ url: URL)