Endpoint to support add accept command

[shanep]

Proposed endpoint

Add the necessary get/put endpoints to support feature request #18 in the cli. This would be from the students perspective not the instructors. Currently all commands in the classroom cli return information using the instructors token.

For this to work for a student, this endpoint would need to return all the classrooms and assignments that a student can access with their own auth token.

Justification

This will be used to implement #18 and make classrooms usable without a student having to use a browser. Lots of schools provide ssh access to local clusters that don't support x11 forwarding so we need tools that are 100% cli to help foster adoption :)