REVERTME: Point requirements file to Django beta

As 1.7.0 is not yet available, add the Django beta to the requirements
file. See https://www.djangoproject.com/download/
Use DATABASE_URL from environment in Travis

- and sqlite *only* in development
Add psycopg to requirements.
Fix an import bug
Merge pull request #7 from sealevelresearch/fix-travis-django-1.7

Get Travis tests working