Fill in missing enrollment activity data.

  * this fixes a visual problem in the chart where the labels are repeated and don't line up

Old:
![labels-off](https://cloud.githubusercontent.com/assets/5265058/4775818/be0b7b0e-5bbb-11e4-8a95-daef504a5ea7.png)

New:
![labels-fixed](https://cloud.githubusercontent.com/assets/5265058/4775819/c4bba3d4-5bbb-11e4-912e-53a5681e3403.png)

@rocha @clintonb @lamagnifica @shnayder