Some test classes have been refactorized for a more consistent use of
the OwnersDataset class and for a simpler test implementation.

This matchers makes the Response status easier to check in tests.

The REST layer has been added but with incomplete tests. Students will
have to complete the tests.

This commit includes an important refactorization regarding tests. Test
classes and datasets have been moved from the "service" project to a new
"tests" project. This way, any project can include this "tests" project
as a dependency in order to have access to these common testing
resources.