(WIP) 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
Yes, I think this is one of the cases where I am getting registration emails for a course I am already registered in. I had specified the same email address with a different username.

It isn't possible for the same email address to be linked to 2 different accounts. It would just be cleaner to error if the username does not match the email address (and not attempt to enroll the student in the course).