Switched to models from Jessykate's project

I decided that, rather than re-inventing the wheel entirely, it would be best to used the models file from Jessykate's django-survey project (https://github.com/jessykate/django-survey/blob/b5aec9097d4bcbf9201d817744749e23f374e9b1/survey/models.py) and adapt it to include the extra fields required.