Updated course index page with feedback link and updated copy.

@rocha @clintonb 

FYI: @shnayder @lamagnifica 

![screen shot 2014-09-30 at 5 04 39 pm](https://cloud.githubusercontent.com/assets/5265058/4466525/8a3a953c-48e5-11e4-8a6a-e189a12b2003.png)

I moved a few of the shared assertions into `AssertMixin`, created a new `assertValidFeedbackLink ` method used in `_test_footer` in addition to `test_course_list`.