ActivityIndicator size problem

### Problem description
In the [new fetch() example script](https://github.com/eclipsesource/tabris-js/blob/master/examples/fetch/fetch.js) next things happening after a user clicking on the Reload Geo-Data button:
1. TextView and Reload Geo-Data button are getting destroyed
2. New ActivityIndicator appears
3. New data loaded from a remote server
4. New TextView and Reload Geo-Data button created
5. ActivityIndicator destroyed

So, on step 4 new TextView and Button appearing on the screen on the same time with the ActivityIndicator.

I can't screenshot that process because it's happening pretty fast, but basically, new page interface is appearing below ActivityIndicator(at the bottom of the page) and then "jumping" at the top of the page after ActivityIndicator is destroyed.

### Expected behavior
I know that this particular issue is a result of the simple mistake in the example code.
But I think that ActivityIndicator widget can really use optional property like "fullscreen: 0/1".

### Environment
- Tabris.js version: 2.6.1
- Device: Lenovo Tab 3
- OS: Android 6.0

### Code snippet
https://github.com/eclipsesource/tabris-js/blob/master/examples/fetch/fetch.js