The double persistence.xml in JSF and REST projects was causing
problems in some environments, as the tables were created twice.

This commit fixes this error by moving the persistence.xml to the
service layer.

The REST API methods for entity creation and modification have been
simplified with more basic entities.

In addition, the UserResource class has been added so that it is
possible now for clients to use it for user authentication.

Some JavaDoc errors detected in the entities have been fixed.

The project dependencies have been updated, including a change from
WildFly 8.2.1 to 10.1.0. This change affects the project configuration
in several ways, specially in tests configuration.

The README.md file has been updated to reflect the configuration
changes.

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.