code: public GrailsClass addOverridableArtefact(String artefactType, @SuppressWarnings("rawtypes") Class artefactClass) {
          return addArtefact(artefactType, artefactClass, true);
      }
docs: Adds an artefact of the given type for the given Class.
  
  @param artefactType  The type of the artefact as defined by a ArtefactHandler instance
  @param artefactClass A Class instance that matches the type defined by the ArtefactHandler
  @return The GrailsClass if successful or null if it couldn't be added
  @throws GrailsConfigurationException If the specified Class is not the same as the type defined by the ArtefactHandler
  @see grails.core.ArtefactHandler