Enrollment API Cleanup

This PR will capture the following work
* Update to version 1
* Change URL scheme to match other APIs
* Add Course Enrollment Detail entry point
* Use Class Based DRF views

@ormsbee @wedaly This should be ready for review. 

In this case, the user must be specified to look up a user's enrollment in a specific course. The idea being that a user and course id is a unique pairing that is used as a tuple to look up a specific enrollment.