Switch demo code to beta.ckan.org

[sharlagelfand]

Registration to https://demo.ckan.org/ has been disabled (#181 (comment)), which makes it difficult / impossible to set things up and test on there! But https://beta.ckan.org/ has open registration, so we can create accounts and get API keys from there and then test on that instance instead.

This issue is to track switching over existing demo code / examples / test setup (e.g. prepare_test_ckan) over to beta from demo.