Behind-the-scenes objects; main object security rules are enough.

Will be done better (more cases handled, more comments) by grafting rev
d11003bb260b.

When binding a dimension to a model, if there is a 'False' value instead of a
parent code, when seeking one, no ID must be extracted.

The override of the 'create' method must return an ID, when binding a dimension
to a model.

Updated the change log.

created analytic code name, is not immediately filled in the first write
processes, and only filled afterwards.

the 'extract_values' method.
This method was used to propagate the analytic codes of a specific object to
another one on the common dimensions.

instruction was missing.

(There are cases where the dictionary var is actually None...)

xcg/oemetasl is now obsolete. We are going to prefer mixins instead. As we no
longer have any other metaclass than this one, the metaclass inheritance is no
longer needed.

Changed method to allow having readonly in a view on analytic dimensions placeholder so that all analytic fields will get readonly too.