[TIMOB-19979] iOS: Improvements on the ti.urlsession module

var urlSession,sessionConfig,session;

function doClick(e) {
    urlSession = require("com.appcelerator.urlSession");
	sessionConfig = urlSession.createURLSessionBackgroundConfiguration("com.appcelerator.session");
	session = urlSession.createURLSession(sessionConfig);
	urlSession.backgroundDownloadTaskWithURL(session, "http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_50mb.mp4");
	urlSession.backgroundDownloadTaskWithURL(session, "http://www.sample-videos.com/video/mp4/480/big_buck_bunny_480p_50mb.mp4");
}

function doClick2(e){
	urlSession.invalidateAndCancel(session);
}

$.index.open();

Ti.App.iOS.addEventListener('downloadprogress',function(e){
	Ti.API.info(e.type);
});
Ti.App.iOS.addEventListener('downloadcompleted',function(e){
	Ti.API.info(e.type);
});
Ti.App.iOS.addEventListener('sessioncompleted',function(e){
	Ti.API.info(e.type);
});

<Alloy>
	<Window class="container">
		<Label id="label" onClick="doClick">Click to initiate two tasks</Label>
		<Label id="label2" onClick="doClick2">Click to cancel two tasks</Label>
	</Window>
</Alloy>

".container": {
	backgroundColor:"white"
}

"Label": {
	width: Ti.UI.SIZE,
	height: Ti.UI.SIZE,
	color: "#000"
}

"#label": {
	font: {
		fontSize: 12
	},
	top:50
}

"#label2": {
	font: {
		fontSize: 12
	}
}