Draft: Illustrate dependency injection

This is just a draft to show how to inject a database service into the main view model. I took this from the Avalonia docs at https://docs.avaloniaui.net/docs/guides/implementation-guides/how-to-implement-dependency-injection and made sure it works.

However, this adds a project reference to the Mesap model project and I do not like this. Maybe there is a way to avoid that using reflection?

Please check this out and let me know what you think! (No need to approve as this PR will not get merged.)