JS: synchronize the undo/redo methods in GUIFrame
JS: synchronize the undo/redo methods in GUIFrame

Synchronization is necessary because inputs can be set from both
the main thread and the AWT thread which is used by the various window
listeners.

Signed-off-by: Harry King <409587b9e6671aa0763646191d292852dc49a658@gmail.com>

jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim,jaamsim/jaamsim