[TIMOB-5466] iOS: Expose Current Window of Tab in Tab Group

   /*
    To keep track of and clean up windows that have been opened on a specific tab, you must do the following:
    - Whenever you open a window, use the "openInTab(tab, win)" function.
    - On every window, listen for its "close" event and call the "trackClosedWindow(tab, win)" function.
    - Whenever you want to close all but the root window of a tab, call the "closeAllInTab(tab)" function.
    */
   
   function openWindowOnStack(i) {
       var win = Ti.UI.createWindow({
           title: 'Window ' + i,
           rightNavButton: Ti.UI.createButton({ title: 'S2: Touch Me' })
       });
       win.rightNavButton.addEventListener('click', function() {
           closeAllInTab(tab);
       });
       win.addEventListener('open', function(evt) {
           Ti.API.info('Opened: ' + evt.source.title);
           if (i < 4) {
               openWindowOnStack(i + 1);
           }
       });
       win.addEventListener('close', function(evt) {
           Ti.API.info('Closed: ' + evt.source.title);
           trackClosedWindow(tab, evt.source);
       });
       openInTab(tab, win);
   }
   
   var outer = Ti.UI.createWindow({
       title: 'Root Window',
       rightNavButton: Ti.UI.createButton({ title: 'S1: Touch Me' })
   });
   outer.rightNavButton.addEventListener('click', function() {
       openWindowOnStack(0);
   });
   
   function trackClosedWindow(tab, window) {
       var windows = tab.windows || [];
       // Iterate through backwards because windows further down the tree are more likely to be removed.
       for (var w = windows.length - 1; w >= 0; w--) {
           if (windows[w] == window) {
               windows[w] = null;
               windows.splice(w, 1);
               break;
           }
       }
       tab.windows = windows;
   }
   function closeAllInTab(tab) {
       var windows = tab.windows || [];
       // Iterate through forwards because we want to close the most recent window last for a nice animation to the root.
       for (var w = 0; w < windows.length; w++) {
           windows[w].close();
           windows[w] = null;
       }
       tab.windows = windows = [];
   }
   function openInTab(tab, window) {
       var windows = tab.windows || [];
       windows.push(window);
       tab.open(window);
       tab.windows = windows;
   }
   
   var tabGroup = Ti.UI.createTabGroup();
   var tab = Ti.UI.createTab({
       window: outer
   });
   tabGroup.addTab(tab);
   tabGroup.open();