[TIMOB-1855] Performance Gains Using TabGroup instead of Window

Doing a normal window operation in an app like this yields a much slower app (slower as in UI rendering, modals opening and closing, views in a ScrollableView, etc.):

var mainWindow = Titanium.UI.createWindow({ ... });
mainWindow.open();

...than this, which makes the app much faster:

var tabGroup = Titanium.UI.createTabGroup();
var mainWindow = Titanium.UI.createWindow({ 
   navBarHidden:true, 
   tabBarHidden:true 
});
var tab = Titanium.UI.createTab({ 
   window:mainWindow 
});
tabGroup.addTab(tab); 
tabGroup.open();

Both produce the same visual result, but I see significant performance gains using the invisible tabGroup option.

I have tested this on multiple applications both in the simulator and on a device. This is for iPhone only.

Hopefully this is helpful.