CSS rule to disable text selection highlighting on editor window

I added this css rule to `body` on `cats.css` file to disable text selection highlighting on editor window.

```css
body {
    ...
    -webkit-touch-callout: none;
    -webkit-user-select: none;
}
```

![cats_text_selection_highlighting](https://f.cloud.github.com/assets/373936/248428/f2d04728-8b0d-11e2-8dbf-7dd35f2d2cbd.png)