Set status item title.

This is my very first lines of Objective-C, so please bear with me. What I want to achieve is something like this:

```js
MacGap.StatusItem.create({title: '00:00', titleSize: 8});
```

```js
MacGap.StatusItem.title = '00:01';
```

The titleSize property is not implemented, I guess that involves using JSContext which is a bit over my head.

I also played with styling the title with html/css (see https://github.com/thecodepath/ios_guides/wiki/Generating-NSAttributedString-from-HTML) but I decided against it since I couldn't find a good way to use the OS X system font (especially since Mavericks uses ".Lucida Grande UI").