Update UA stylesheets for lists

#1232

Servo UA (http://www.w3.org/TR/CSS21/sample.html)

This is UA css from http://mxr.mozilla.org/mozilla/source/layout/style/html.css and http://dev.w3.org/csswg/css-lists/#ua-stylesheet

```
ul margin-left: 40px -> padding-left: 40px
ol margin-left: 40px -> padding-left: 40px
```