adding django migrations support

[francofuji]

No description provided.

[kaedroho]

It's probably better to rename the south migrations folder to south_migrations (South will detect this in 1.0 and above, so update that in install_requires) and name the django migrations folder migrations. This way it will continue to work in both environments without extra settings.

[czpython]

@francofuji please use migrations for django migrations and south_migrations for the old south migrations.