mnemonic_activate
Description:
The default handler for this signal activates widget if group_cycling is false, or 
      just makes widget grab focus if group_cycling is true.
Parameters:
| group_cycling | 
           true if there are other widgets with the same mnemonic  | 
      
Returns:
| 
           true to stop other handlers from being invoked for the event. false to propagate the event further.  |