#53 - Refactored various components:

- updated the authentication coordinator to use async await
- replaced the UserSession with a ClientProxy (similar to the RoomProxy)
- renamed `completion` to `callback` on the coordinators and view models
- renamed `viewModelResult` to `viewModelAction`
- introduced back UserSession as a user specific service container

ElementX/Sources/Services/Session/UserSessionProtocol.swift

@@ -0,0 +1,14 @@
+//
+//  UserSessionProtocol.swift
+//  ElementX
+//
+//  Created by Stefan Ceriu on 27/05/2022.
+//  Copyright © 2022 element.io. All rights reserved.
+//
+
+import Foundation
+
+protocol UserSessionProtocol {
+    var clientProxy: ClientProxyProtocol { get }
+    var mediaProvider: MediaProviderProtocol { get }
+}