Django-reversion templates and some minor improvements

Hi Douglas,

I have some more additions, feel free not to merge some of them if they're too specific to my project needs.

* In some situations, the save button is the only button on the page when changing an object. A little check makes it `btn-primary` in that case.
* The first column of a `TabularInline` looked a bit weird, because it got the header of the first attribute. When an object already exists, Django puts the `__unicode__` representation there. I just gave it an empty `<th></th>`.
* Removed a `table-striped` so the `TabularInline` looked less cluttery.
* I added templates for the [django-reversion](https://github.com/etianen/django-reversion) and [django-reversion-compare](https://github.com/jedie/django-reversion-compare) apps.

Regards, Erik-Jan