Add Unit Tests

[rotexdegba]

• Add Unit Tests, look at how Slim and Laravel are doing it
• Look into using example in https://akrabat.com/testing-slim-framework-actions/ & https://github.com/slimphp/Slim-Skeleton/tree/main/tests for writing unit tests for actions
• The easiest approach is to run http GET & POST requests for all the routes that come with a vanilla installation of this project and verify that the returned Response has the right status code & that the return Body contains the expected elements

[rotexdegba]

• All routes are now tested as of version 5.0.1 see https://github.com/rotexsoft/slim-skeleton-mvc-app/compare/5.0.0...5.0.1