WL-98 As a course instructor, auto-register (as well as auto enroll) a list of students into my course

@chrisndodge here are the changes related to WL-98 for your quick reivew. 
we have written the test cases but only one coverage is missing in our code.  
currently we did not check/test the code for quality.

In order to test this feature you need to set the flag: 
FEATURES['ALLOW_AUTOMATED_SIGNEDUPS'] = True
Nit: could create a helper method that verifies the expected status_code, # of row_errors, # of warnings, and # of general_errors (to remove code duplication of lines 319-323).

Along the lines of _verifiy_response(expected_status_code, exepcted_row_errors, expected_warnings, expected_general_errors).