Fix object-tools to allow for more than one link

First off, thanks for the best django admin bootstrap app I could find. Really nicely done. :)

We use django-reversion to track object changes and it adds a link to the `object-tools` section of the changelist. Currently it looks like this:

![Screen Shot 2013-01-23 at 9 55 51 PM](https://f.cloud.github.com/assets/1594130/92445/acc19338-65d1-11e2-8244-c2cf6c52b566.png)

This pull request adds the necessary css to make the buttons align horizontally and also monkey patches the `btn` class onto all the links, because django-reversion doesn't add it.

![Screen Shot 2013-01-23 at 9 56 17 PM](https://f.cloud.github.com/assets/1594130/92446/b11151c6-65d1-11e2-9cc2-e49d451b017e.png)