Added course enrollment

Change-Id: I973fcb2672b53e0aa64158bea46b8cbb9c371c17

@rocha 
It is pretty easy to use, check `setup.py` and `setup.cfg` in https://github.com/edx/analytics-tasks.

For requirements, just make sure there is a `requirements.txt` in the same folder as `setup.py`.

The only advantage is that we standardize a little bit how we are doing `setup.py` across our repos. Right now they have been slowly drifting away, which makes working across them a little bit harder.