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. 

api.py will allow enrollment modification, assuming it is used in-process. The views.py will only allow you to create a new enrollment with the defaults, where mode=honor. If the course does not have an honor mode, api.py checks the available modes, throws an error, and lists the available modes.