add a function to refresh IosList#elems

just in case any are dynamically added or removed.
make IosList accessible to window

To allow other javascript code to actually invoke .refreshElements. This means, if you want refreshElements functionality, you need to manually initialize an IosList instance, like so:

```
var ioslist = new IosList($('#my-ios-list'));

$('#something').on('ajax:success', function() {
  ioslist.refreshElements();
});
```
I'd be pretty open to doing this another way, though.