Camel-8024 Camel-sjms improvement to JMSMessageHelper

Hi,

This PR is related to: https://issues.apache.org/jira/browse/CAMEL-8024

as Aaron Whiteside noted in the ticket https://issues.apache.org/jira/browse/CAMEL-7949 that patch breaks byte[] support.

I think I've fixed that and improved JMSMessageHelper.

Andrea