And, Patch changeObjectClass extension to remove useless attributes

Copying __dict__ from one object to another brings us to situation where
we don't have many objects which we don't need at all, for example, migrating
objects with subclasses who were initially OFS objects and later an ERP5
object can lead to adding subobjects as attributes of the new object, which
is completely undesirable. To handle this, it is important to delete the
sub-objects as the attributes for those migrated classes.

Old Catalog Tool didn't have portal_type attribute, so while migrating
via synchronizeDynamicModule, after _bootstrap, we expect the tool to
have a portal_type to finalize migration.

This step is now being done only at the end of _bootstrap after we
change the classes for portal_catalog and its sub-objects.