All tours - make first stop a clear tour intro

We should have an established style for the first tourstop (which acts as a"splash screen") for our tours. This might be helped if we can implement https://github.com/OneZoom/OZtree/issues/781, and even more if (eventually) we implement https://github.com/OneZoom/OZtree/issues/807.

Related to comments by @wolfmanstout at https://github.com/OneZoom/OZtree/issues/768