Switch from AirTable to Baserow to fix leaking API key issue

[tanius]

So far, the AirTable API key has been included in the code of this repo (here and here). That's a security issue, and as a permanent fix we decided to move from AirTable to Baserow, an open source alternative that allows to configure write-only API keys. Details here.

Just putting in this issue as a reminder of what has to be done to make the associated website functional again.