[TIMOB-6151] Label shadow - blur and opacity properties

Ti.UI.Label has the properties shadowColor and shadowOffset. It would be nice if it also supported setting the blur and opacity of the shadow. This is useful when you don't want that hard shadow you get by just setting color and offset. It could instead be a label.shadow property, that takes an object as an argument:

var label = Ti.UI.createLabel({
	shadow: {
		color: '#000',
		offset: {
			x: 0,
			y: 1
		},
		opacity: 0.4,
		blur: 2
	}
});