#325 created method for sending email to external.

Added a method in the school model to send an email to external if there are comments on registration. Haven't tested this, but wanted to get a diff out for the sake of progress.
It'd be nice to include the school name in the subject too:
```python
send_mail(
    'Registration comments from ' + school.name,
    school.name ' made some comments about registration:' +
    school.registration_comments,
    ...)
```