[TIMOB-4366] iOS: Support Ti.UI.createNotification

Feature

Android has support for toast notifications through the method "Ti.UI.createNotification". We can expand this to support iOS as well, and add documentation to the APIDocs. I'm aware this isn't a native feature of iOS, but it's still something useful we could offer our users. And it shouldn't be too difficult to do, because we already show similar notifications in the kitchen sink using [pure JavaScript](https://github.com/appcelerator/titanium_mobile/blob/master/demos/KitchenSink/Resources/app.js#L103).

Sample Code

The following works on Android:

Ti.UI.createNotification({ message : 'Hello, World!' }).show();

Associated Helpdesk Ticket

http://appc.me/c/HNU-68239-489