ID not returned when webapp item created

Code to reproduce:

```
var webAppItem = new BCAPI.Models.WebApp.Item('Equipment', {
    'name': (new Date).getTime(),
});

webAppItem.save({
    success: function(item) {
        console.log(item.get('id')); //undefined
    },
    error: function(jqXHR) {
        var test = jqXHR;
    }
});
```
