do not show add slider and pane if ios native scrolling is on and supported

Hello,

This is cleaned version of my another PR  #107. 

I've added separate tests for iOS version only. [Yeti](https://github.com/yui/yeti) eases the process of testing. I've run like this:

```bash
$ grunt default build:tests && yeti tests/SpecRunneriOS.html
```

If this PR passes I think it should be noticed somewhere that .pane and .slider classes are not created when `iOSNativeScrolling` is used.