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/ServerProtocol.swift

@@ -7,3 +7,27 @@
 //
 
 import Foundation
+
+protocol Server
+{
+    var connected: Bool { get }
+    
+    /// Designated initializer. Takes an API endpoint URL
+    init(_ url: URL)
+    
+    /// Attempts to connect to the server at the specified endpoint.
+    func connect(_ completion: @escaping (Error?) -> Void)
+    
+    /// Sets server's state as "disconnected"
+    func disconnect(_ completion: (Error?) -> Void)
+    
+    /// Fetches a list of all currently configured devices for this server, or returns an error.
+    func fetchDevices(_ completion: @escaping (Result<[AnyDevice], Error>) -> Void)
+    
+    /// Tells the server to set the state of a given device to the given state
+    func toggleDevice(_ device: AnyDevice, state: DeviceState, completion: @escaping (Error?) -> Void)
+    
+    /// Returns true if this is a device this server is responsible for
+    func responsibleForDevice(_ device: AnyDevice) -> Bool
+}
+