Add initial South migrations (#264)
Branch: feature/264-south-initial-migrations
Refs #264: Add doc about adding South

In release notes, mention that South support has been added,
and give instructions for getting start with it.
Refs #264: remove httptester migrations

... on the assumption that #328 is going in.
Merge branch 'feature/bulk-messaging-api' into feature/264-south-initial-migrations

Hoping to fix Travis test failures.
`python manage.py` not `manage.py`
Merge branch 'feature/bulk-messaging-api' into feature/264-south-initial-migrations

# Branch: feature/264-south-initial-migrations
Refs 264: Convert database backend to south

And get rid of old migration files from 'db' backend.
Merge pull request #264 from rapidsms/feature/264-south-initial-migrations

Add south initial migrations