ServerMultiplex: Introduces a server mutiplexer

- Also moves all the existing Wemo* stuff over to support the multiplexer
- Moves MainViewController to be the owner of the multiplexer, and its delegate

XIONControlPanel/Servers/WemoServer.swift

@@ -22,8 +22,10 @@ enum ConnectionError : Error
     case serverUnavailable
 }
 
-class WemoServer
+class WemoServer : Server
 {
+    private var devices: [WemoDevice] = []
+    
     fileprivate(set) var baseURL:    URL
     fileprivate(set) var connected:  Bool = false
     
@@ -31,7 +33,7 @@ class WemoServer
     fileprivate var _errorStream:    StandardErrorOutputStream = StandardErrorOutputStream()
     fileprivate var _operationQueue: OperationQueue = OperationQueue()
     
-    init(_ url: URL)
+    required init(_ url: URL)
     {
         self.baseURL = url
         
@@ -68,29 +70,32 @@ class WemoServer
         completion(nil)
     }
     
-    func fetchDevices(_ completion: @escaping ([WemoDevice], Error?) -> Void)
+    func fetchDevices(_ completion: @escaping (Result<[AnyDevice], Error>) -> Void)
     {
         if (self.connected) {
             let op = FetchDevicesOperation(baseURL: self.baseURL, session: _urlSession)
             weak var weakOp = op
             op.completionBlock = {
-                guard let strongOp = weakOp else { completion([], nil) ; return }
+                guard let strongOp = weakOp else { return }
                 if let error = strongOp.error {
                     self._logError("Error fetching devices", error: error)
+                    completion(.failure(error))
+                } else {
+                    self.devices = strongOp.devices
                 }
                 
-                completion(strongOp.devices, strongOp.error)
+                self.devices = strongOp.devices
+                completion(.success(self.devices.map { AnyDevice($0) }))
             }
             _operationQueue.addOperation(op)
         } else {
-            let err = ConnectionError.serverUnavailable
-            completion([], err)
+            completion(.failure(ConnectionError.serverUnavailable))
         }
     }
     
-    func toggleDevice(_ device: WemoDevice, state: WemoDevice.State, completion: @escaping (Error?) -> Void)
+    func toggleDevice(_ device: AnyDevice, state: DeviceState, completion: @escaping (Error?) -> Void)
     {
-        if (self.connected) {
+        if self.connected, let device = findDevice(device) {
             let op = ToggleDeviceOperation(baseURL: self.baseURL, session: _urlSession, device: device, state: state)
             weak var weakOp = op
             op.completionBlock = {
@@ -108,12 +113,22 @@ class WemoServer
         }
     }
     
+    func responsibleForDevice(_ device: AnyDevice) -> Bool
+    {
+        return self.devices.contains { $0.serial == device.serial }
+    }
+    
     // MARK: Internal
     
     internal func _logError(_ description: String, error: Error)
     {
         print("ERROR: \(description) \(error)", to: &_errorStream)
     }
+    
+    internal func findDevice(_ device: AnyDevice) -> WemoDevice?
+    {
+        return self.devices.first { $0.serial == device.serial }
+    }
 }
 
 internal class WemoOperation : Operation
@@ -188,9 +203,9 @@ internal class FetchDevicesOperation : WemoOperation
 internal class ToggleDeviceOperation : WemoOperation
 {
     var device: WemoDevice
-    var state:  WemoDevice.State
+    var state:  DeviceState
     
-    init(baseURL: URL, session: URLSession, device: WemoDevice, state: WemoDevice.State)
+    init(baseURL: URL, session: URLSession, device: WemoDevice, state: DeviceState)
     {
         self.device = device
         self.state = state