* Remove all `DEMO_*` fixtures from .env.tpl
* Add TEST_PROJECT and TEST_KEYCLOAK_USER/PASSWORD variables
* Replace DEMO users with TEST user in realm-export.json.tpl
* Regenerate xnat.sql.tpl without any subject data
* Remove sse, ta and keytray .sql.tpl files, we can test without these
  fixtures
* Modify docker-compose files to reflect these changes
* Tweak tests to work with new fixture environment