Twitter Bootstrap Add/Edit: One primary button, style cancel button as btn-warning

There should only be one primary button, or none at all. I chose to make the "save and go back to list" button the primary button if it's present and the  "save" button otherwise.

I also have given the "cancel" button the class `btn-warning`. See [here](http://getbootstrap.com/2.3.2/base-css.html#buttons) for the looks of this button.