HOTFIX - implement one to one relation between
sponsor and sponsor profiles properly.

calpoly/frontend/sponsors.py: first_or_404() for
sponsor_profile.
calpoly/sponsors/models.py: Add one-to-one
relation.
renamed:    migrations/versions/3637c71e7eea_add_sponsors_tables.py -> migrations/versions/4e69e486a166_add_sponsors_tables.py