Nuke migrations: start over again.

Something went wrong, I couldn't resolve it. There are no live databases
anywhere so just nuke the migrations and start again.
Merge pull request #6 from sealevelresearch/nuke-migrations

Nuke migrations: start over again.
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