Define prestart attribute on ButtonMark to place buttons before start

item.py

@@ -42,6 +42,9 @@ class Item:
     def get_next_button(self):
         return self._timings.get_button()
 
+    def is_button_prestart(self, name):
+        return self._timings.is_button_prestart(name)
+
     def get_title(self):
         return self._title