[TIMOB-27853] Add ability to detect that screenshot was taken on iOS

   Ti.App.iOS.addEventListener('screenshotcaptured', function() {
       Ti.API.info('screenshotcaptured');
   });
   

   
   var win = Ti.UI.createWindow({
       backgroundColor: '#fff'
   });
   
   win.open();
   
   Ti.App.iOS.addEventListener('screenshotcaptured', function() {
       Ti.API.info('screenshot captured');
   });