Add toString functionality to entities to make the variables information in the debugger more insightful

Now, if we debug an application and a value of an object is an object, we see an ID in the variables pane. This is not always very informative.

It would be nice if you could show something else, just like you have in many IDEs when developing for other programming languages (for example, in IntelliJ, when you implement an toString method in your Java class, you see the result of the toString).

So, say you have a Course object with a Teacher, it would be great if you:

1. Could define a toString method for Teacher that returns e.g., the full name of the teacher 
2. The debugger shows the, in this case, full name of the teacher when you investigate the Course