Modernizes the way body validation works

Body validators implement the BodyValidator interface.
In case of errors, ValidationExceptions are stored in a List.
Therefore, new methods validate(List<ValidationException>) have been created in JimpleBody and Body.
In order to allow IDEs to mark the respective parts of the code, ValidationException carry additional information about the concerned object.

Is trying to retain backwards compatibilty: The old validation methods use their respective Validator and throw the first exception in the list. The old message texts are kept.