Migrated from Function-Based Views to Class-Based-Views

@chrisndodge @antoviaque @ziafazal, I've converted the api_manager implementation over to Django REST Framework's "Class-Based Views" (http://www.django-rest-framework.org/tutorial/3-class-based-views) as a step towards an eventual merge with edx/edx-platform.  

I've rebased my changes against solutions/master and addressed a couple of conflicts that arose in the sessions area having to do with the new login security.  Everything appears to be in order and the tests are all passing, but Zia you may want to take a look just to be sure.