Fix form for full width of column

I noticed the add user form was formatted in such a way that it did not fill the entire width of the column it was in. I've made a small adjustment here to correct this.

Before this change: http://i.imgur.com/aFbBaGI.jpg
After this change: http://i.imgur.com/16rpy1T.jpg

On an unrelated note: is there any interest in having a Vagrantfile for setting up a local dev vm? I have one that I can submit a pull request for if so.