beforeTabClose
beforeTabClose
    Called after the user clicks to close any dynamic tab, immediately before closing it. 
The event listener function may return
    
     false
    
    to veto the tab page close.
   
Parameters:
- 
     
tabPanel(reference): this tab panel reference; - 
     
     
     
tabName(String): name of the tab page to be closed; 
    
     
     Example:
    
   
    This event listener is auto-wired according to a naming convention ("
    
     panelId_eventType
    
    "):
   
    tabs_beforeTabClose: function() {
    
    ...
    
    }
   
    
     
    
   
