Add support for starting and stopping the tunnel

This commit introduces the Tunnel view model object which has
support for asking for permission, starting and stopping the
tunnel. It automatically updates its state and publishes
changes as an ObservableObject.

Apple/App/Status.swift

@@ -0,0 +1,43 @@
+import Foundation
+import NetworkExtension
+
+extension Tunnel {
+    enum Status: CustomStringConvertible, Equatable, Hashable {
+        case unknown
+        case permissionRequired
+        case disabled
+        case connecting
+        case connected(Date)
+        case disconnecting
+        case disconnected
+        case reasserting
+        case invalid
+        case configurationReadWriteFailed
+
+        var description: String {
+            switch self {
+            case .unknown:
+                return "Unknown"
+            case .permissionRequired:
+                return "Permission Required"
+            case .disconnected:
+                return "Disconnected"
+            case .disabled:
+                return "Disabled"
+            case .connecting:
+                return "Connecting"
+            case .connected(_):
+                return "Connected"
+            case .disconnecting:
+                return "Disconnecting"
+            case .reasserting:
+                return "Reasserting"
+            case .invalid:
+                return "Invalid"
+            case .configurationReadWriteFailed:
+                return "System Error"
+            }
+        }
+    }
+}
+