Updated Enrollment Filling

- Filling with data from previous day, not next day
- Cloning the original datapoint instead of creating an empty one. (This will be more useful for enrollment tracks)
- Added a separate test for testing the filling algorithm. (Dealing with gaps for all test data is an unnecessary pain)
Displaying Enrollment Mode on Enrollment Activity Page
Merge pull request #169 from edx/verified-enrollment

Displaying Enrollment Mode on Enrollment Activity Page