Remove 'south' and its migrations.

https://docs.djangoproject.com/en/1.7/topics/migrations/#upgrading-from-south
Refactor code to fix migration serialization issues.

Django migrations using Python 2 fails to serialize unbound methods,
so they recommend to move methods for upload_to and similar to live
in the main module body, rather than the class body.
https://docs.djangoproject.com/en/1.7/topics/migrations/#serializing-values
Make new initial migrations in the new format (Django migrations).
Fix admin.E108 error while dinamic add sliver ifaces.
Upgrade dependencies to Django 1.7