#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/Screens/HomeScreen/HomeScreenModels.swift

@@ -17,7 +17,7 @@
 import Foundation
 import UIKit
 
-enum HomeScreenViewModelResult {
+enum HomeScreenViewModelAction {
     case logout
     case selectRoom(roomIdentifier: String)
 }