compound joysticks, button guide in screens, improve API

src/testmod/java/dev/isxander/controlify/test/ClientTestHelper.java

@@ -73,8 +73,8 @@ public class ClientTestHelper {
             }
 
             @Override
-            public String guid() {
-                return "FAKE";
+            public int joystickId() {
+                return -1;
             }
 
             @Override