create quickstart data loading command for development / testing purposes

[florisdenhengst]

It is tedious to always have to create super users, run migrations, and browse to /admin and manually create runners and consent forms.

As a user, I want to be able to

pip install sharpie
sharpie-web quickstart
# ... install a use case e.g. python install.py mountain
sharpie-web runserver

The quickstart command should:

• create a superuser with default username/password values
• run the migrations
• create a runner with a default connection key
• create a consent form
• do any other work that is necessary before installation

This should be used only in development / testing mode as it will load default.
The defaults should be reflected in the quickstart in docs/usage and in the README.md