Implementation of event handling

• AWT toolkit installs Motif Peers for all Component objects.
• Callback function added to some callbacks (e.g XmNactivateCallback for PushButton).
• Callback function invokes method such as action() of Motif Peer class.
• AWT Peer method calls postEvent() for the Component object.
• AWT toolkit calls handleEvent() for the object and its parent widgets while it returns false