[TIMOB-26507] Windows: View.center is not respected when left & top is set.

center property is not respected when left and top is set. Even when these properties are already set, center should be respected and update the position of the view. Also, we should be able to use undefined to "clear" existing values according to [UNDEFINED behavior](https://docs.appcelerator.com/platform/latest/#!/guide/UI_Composite_Layout_Behavior_Spec-section-src-4196675_UICompositeLayoutBehaviorSpec-UNDEFINEDbehavior) which is taken care by TIMOB-26507.

var win = Ti.UI.createWindow({
    backgroundColor: 'green'
});

var view1 = Ti.UI.createView({
    width: 100, height: 100,
    top: 100, left: 100,
    backgroundColor: 'blue',
});

win.addEventListener('click', function (e) {
    // view1.top  = undefined;
    // view1.left = undefined;
    view1.center = { x: e.x, y:e.y };
});

win.add(view1);
win.open();

Expected: View should move to the position where you clicked.