Tutorial for testing in devon4j

[GuentherJulian]

Create a new tutorial that shows how testing is done in devon4j.

Idea:

1. Install devonfw-ide
2. Create a Java project
3. Create an entity, a REST service and implement some logic (e.g. for finding and saving new objects of the entity)
4. Create a module test for testing the logic
5. Create a subsystem test for testing the REST service

Helpful links:
https://github.com/devonfw/devon4j/blob/master/documentation/guide-testing.asciidoc
https://github.com/devonfw/jump-the-queue/tree/master/java/jtqj/core/src/test