refactor(ISenderHandler): Umbenennung in IAuthSenderHandler.

- umbenannt in SendMessageAsync als SendKeyAsync

DigitalData.Auth.Tests/Client/AuthClientTests.cs

@@ -111,7 +111,7 @@ public class AuthClientTests
         string message = "message";
 
         // Act
-        await sender_client.SendMessageAsync(user, message);
+        await sender_client.SendKeyAsync(user, message);
 
         // delay fort getting answer
         await Task.Delay(2000);