consistent list button

The instance overview page looked strange because there were so many lines for no obvious reason. This fixes that by adding top- and bottom margins to both `hr` and `.list_button`.

While I worked on that I also refactored the general use of `list_button` as well as the general placement of these buttons. e.g. I changed the norms index to look more like the proposal index:

Before:

![2013-07-20-121153_1440x900_scrot](https://f.cloud.github.com/assets/202576/830048/1d1aabfe-f125-11e2-8cd1-2126a93b8edc.png)

After:

![2013-07-20-121128_1440x900_scrot](https://f.cloud.github.com/assets/202576/830047/12664f2e-f125-11e2-8c58-7a19ba9a4c16.png)