[TIMOB-5208] createWindow method parity

When building a window based app, opening a window (with no properties) in iOS results is a black BG window, where in Android it results in a window with a "spashscreen background" (see attached images, the label is simply added to see the effect, but not needed to reproduce the "issue")

var win = Ti.UI.createWindow();

var label = Ti.UI.createLabel({
    text: 'test',
    color: 'white'
});

win.add(label);

win.open();