Differentiated buttons and made Prev and Next buttons into arrows

#2136 did so by giving the submit button the "btn-primary" class and changed next and prev buttons to use the html button tag so I could use `<em class="icon-arrow-right"></em>`, etc...

Before:
![Screen Shot 2013-02-07 at 3 38 58 PM](https://f.cloud.github.com/assets/3364609/137884/9ff88b3e-717f-11e2-9741-9d78aa8618c2.png)

After:
![Screen Shot 2013-02-07 at 3 39 20 PM](https://f.cloud.github.com/assets/3364609/137885/a4fdb564-717f-11e2-875a-40412c11dc62.png)