Updated dependencies for south migrations

Working on [django-oscar-fancypages](https://github.com/tangentlabs/django-oscar-fancypages) I had some issues with not specifying the migration dependencies correctly. Fixing this caused some issues with Oscar's migrations because it was missing ``depends_on`` declarations. I went through and (hopefully) fix all the missing dependencies.

I ran a fresh database setup with the new migrations and it all ran through fine so it doesn't seem to have introduced any issues. Let's see what Travis says :wink: 

This might also fix #551. 

In case you are interested, the current dependency graph (incl. the changes in this PR) looks like this:

![migrations](https://f.cloud.github.com/assets/1236629/876691/08d3c72a-f8d7-11e2-9a60-45cb3b169272.png)

Generated using: ``./manage.py graphmigrations | dot -Tpng -omigrations.png``