Avoid caching runtime specific objects

* Caching references to visitor, query service and factories is dangerous
  since these can hang around in their parent objects after a change of
  server version and cause class cast exceptions

* SqlTransformationMappingRootValidationRule
 * Especially important with this class since it is create as a singleton
   static and used throughout the life of the application
Merge pull request #92 from phantomjinx/master

More reference caching removel