[AS7-6334] messaging resource transformers refactoring

* move resource transformation code from MessagingExtension
  into a separate MessagingTransformers class
[AS7-6334] messaging: fix resource transformation

* give sensible names for constants identifying new attributes or attributes with expression
  support added after management version 1.1.0
* add transformation and expression rejection tests against AS7
  7.1.3.Final artifacts