Displaying Enrollment Mode on Enrollment Activity Page

![screen shot 2014-10-24 at 3 57 08 pm](https://cloud.githubusercontent.com/assets/910510/4775506/9e6ec7ea-5bb8-11e4-8ac1-9d6ed311a8a8.png)

@rocha @dsjen @marcotuts @shnayder @lamagnifica 
Can `enrollment_modes` constants be used?