(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
the above four lines could just be

```python
chars = [
    char for char in string.ascii_uppercase + string.digits + string.ascii_lowercase
    if char not in 'aAeEiIoOuU1l'
]
````