Install Cairn on Staging

We have credentials for a Tutor Wizard edition. With it, we should be able to insall the cairn plugin.

We'll try it out on Staging, where we can also disable the current Tracking plugin to study its effects on the data gathered by Cairn.

Steps:

1. Activate the license on Staging
   • if you log in at overhang.io with those credentials you'll see the license ID. And if you click it, you can find instructions for activating the license
2. Install the Cairn plugin
   • https://overhang.io/tutor/plugin/cairn
3. Document how Cairn was installed to make the process reproducible.