Cleaner parser web UI data models

[tadhg-ohiggins]

Figure out how we want to store information, particularly in terms of whether we want it in Redis or the Django database, and how to make the Django REST framework be happy with our only including some submitted info in the database models.

• Use django-storages to make this work locally.
• Write docs for how to use django-storages to make this work with S3 storage in a production environment.

This issue is essentially mirrored by eregs/regulations-parser#302.