Create a validation tool

[adrienlauer]

A validation tool should be created. Validation would be based on a ValidationProvider interface like this:

@Facet
public interface ValidationProvider {
    Set<Violation> validate();
}

• This interface can be implemented by plugins that provide validation behavior.
• All plugins implementing this interface should be collected by the validation tool and activated.
• Then the validate() method of each plugin would return the set of violations encoutered.

The Violation interface could be like:

public interface Violation {
    ViolationCode getViolationCode();
    Map<String, Object> getProperties();
}

A merge of ErrorCode and ViolationCode should be considered if useful.