Add a little padding for the install tool license's view

* `system/themes/default/install.css`
* Two screenshots showing the view before and after the change

<p align="center">
<img src="https://f.cloud.github.com/assets/1218766/906013/3963cfc4-fc66-11e2-9f38-0d0c1f4aeedb.png" alt="Before" width="200" height="200">
<span></span>
<img src="https://f.cloud.github.com/assets/1218766/906014/3ed64fc2-fc66-11e2-938f-a50870c66b6f.png" alt="After" width="200" height="200">
</p>