Enable 3rd party to handle violations

[codecholeric]

This adds an API for 3rd party clients to access information about violations.
Up to now, rule.evaluate(classes) didn't give a lot of useful information to react to violations, e.g. for drawing some kind of external report, etc.
Now it's possible to react to certain types of objects, contributing to a violation, like JavaFieldAccess, etc.
The first draft of the API can be used the following way

ArchRule rule = noClasses().should().accessField(System.class, "out");
EvaluationResult result = rule.evaluate(classes);
result.handleViolations(new ViolationHandler<JavaFieldAccess>() {
    @Override
    public void handle(Collection<JavaFieldAccess> violatingObjects, String message) {
        // handle field accesses causing a violation
    }
});

The handler will be notified about all objects of an assignable type, i.e. ViolationHandler<JavaAccess<?>> will be notified about all violations any JavaAccess contributed to, ViolationHandler<JavaMethodCall> will only be notified about violations caused by method calls.