0.9.x adds client code for interacting with UISliders via LPSliderOperation

adds `slider_set_value` for interacting with `LPSliderOperation`.


```
def slider_set_value(slider_id, value,  options = {:animate => true,
                                                   :notify_targets => true})
                                                         
```

which boils down to: 

```
map(query_str, :changeSlider, value_str, *args)
```

see https://github.com/calabash/calabash-ios-server/pull/26