#40: Add basic AuthenticationService and missing UI tests.

* Add MockAuthenticationService and ServerSelectionUITests.
* Add tests covering the Authentication flow.

ElementX/Sources/Services/Client/MockClientProxy.swift

@@ -0,0 +1,39 @@
+//
+//  MockClientProxy.swift
+//  ElementX
+//
+//  Created by Doug on 29/06/2022.
+//  Copyright © 2022 Element. All rights reserved.
+//
+
+import Combine
+import MatrixRustSDK
+
+struct MockClientProxy: ClientProxyProtocol {
+    
+    let callbacks = PassthroughSubject<ClientProxyCallback, Never>()
+    
+    let userIdentifier: String
+    
+    let rooms = [RoomProxy]()
+    
+    func loadUserDisplayName() async -> Result<String, ClientProxyError> {
+        .failure(.failedRetrievingDisplayName)
+    }
+    
+    func loadUserAvatarURLString() async -> Result<String, ClientProxyError> {
+        .failure(.failedRetrievingAvatarURL)
+    }
+    
+    func mediaSourceForURLString(_ urlString: String) -> MatrixRustSDK.MediaSource {
+        MatrixRustSDK.mediaSourceFromUrl(url: urlString)
+    }
+    
+    func loadMediaContentForSource(_ source: MatrixRustSDK.MediaSource) throws -> Data {
+        throw ClientProxyError.failedLoadingMedia
+    }
+    
+    func sessionVerificationControllerProxy() async -> Result<SessionVerificationControllerProxyProtocol, ClientProxyError> {
+        .failure(.failedRetrievingSessionVerificationController)
+    }
+}