Do not catch SlingValidationExceptions in the ValidationServiceImpl.java

Currently all SlingValidationExceptions are caught in the ValidationServiceImpl.java (https://github.com/apache/sling/blob/trunk/contrib/validation/core/src/main/java/org/apache/sling/validation/impl/ValidationServiceImpl.java#L384). Since those exceptions should only happen during development, it would be very good, if those exceptions would not be caught by the ValidationServiceImpl. That way the exception is printed in most of the cases directly into the response (i.e. is easier to see during development time). Also features like a custom exception handler (through a servlet filter) or the AEM error filter could be used to expose that exception.