Feature/2122 exam list page

Hi @aronasorman - some updates for #2122 - Exam list page

I made some fixes:

1. The updates did not toggle the `Disable Exam Mode` back to `Enable Exam Mode` when another button is clicked by the admin/teacher.
1. The page title was not updated when user is on the test page or on the test list page.
1. The nav bar link did not have the nav indicator.  I used the `bootstrap.min.css` but it does not seem to work very well on the nav links.  Please see attached screenshots.  I noticed we did not use the above bootstrap css in any other pages so I will leave it as is and work on the unit test.  Perhaps I can look at this when we have time.

Please review.

![screen shot 2014-06-10 at 4 01 59 pm](https://cloud.githubusercontent.com/assets/175580/3226980/ade3c062-f075-11e3-8208-eb89baca35d0.png)
![screen shot 2014-06-10 at 4 02 10 pm](https://cloud.githubusercontent.com/assets/175580/3226981/ade8a42e-f075-11e3-8a12-57223ed72519.png)

Hi @cpauya, I think we moved to using `show_message` for displaying messages to the user. You can specify in that function on what type of error it is, whether `"error"`, `"success"`, or `"warning"`.