Make sure budgets and slug_helpers migrations are in a package

Otherwise there are some circumstances in which migrations can fail
with errors like:

  south.exceptions.NoMigrations: Application '<module 'pombola.slug_helpers' from '/home/mark/pombola/pombola/pombola/slug_helpers/__init__.pyc'>' has no migrations.

(In that case when there was a leftover __init__.pyc file but no
__init__.py file there.)