ESSENTIALS-979 integrating Bert's and Michiel's changes plus: use parameters; never regenerate originals!

- Remove unused code on imageSets from namespace
- Put back node.getSession().refresh on exception (proven by client issue)
- Put back data.hasProperty(JcrConstants.JCR_DATA)  (proven by client issue)
- Documentation and logging improvements
- Do not do session.save(), rely on CMS to do that