Added "resetcss" method

Hi Adam, many thanks to your nice plugin.
To deal with the case of page height changing dynamically, for example using tab UI (http://jqueryui.com/tabs/), I added "resetcss" method.
Now I can write some code like below.

```
var slidebars = new $.slidebars();
$tabContent.on('tabsactivate', function() {
	slidebars.resetcss();
});
```