- simplifies handling.
  * enables unprotecting to avoid accidentally cloning.
  * removes the need for dedicated constructor or factory forms.
  * simplfies DimensionedField and GeometricField New factory methods

- update objectRegistry management method (internal use)

  old:  bool cacheTemporaryObject(...)
  new:  bool is_cacheTemporaryObject(...)

  to clarify that it is a query, not a request for caching etc.