Add background app refresh support (#892)

* Add background app refresh support

* Cleanup: move methods around so delegates are implemented above privates and privates are ordered better

* Add discardableResult on the userSessionStore's refreshRestorationToken

ElementX/Sources/Services/Client/ClientProxyProtocol.swift

@@ -23,6 +23,14 @@ enum ClientProxyCallback {
     case receivedAuthError(isSoftLogout: Bool)
     case receivedNotification(NotificationItemProxyProtocol)
     case updateRestorationToken
+    
+    var isSyncUpdate: Bool {
+        if case .receivedSyncUpdate = self {
+            return true
+        } else {
+            return false
+        }
+    }
 }
 
 enum ClientProxyError: Error {