refs #413 Decomposed metatype-related functions of CValueObject into a dedicated class Mixin::MetaType,

bypassing the old Policy::MetaType classes. The ultimate intention is to decompose all the aspects of
CValueObject into separate mixins in this manner, and have derived classes inherit from the mixins directly.
Splitting the responsibilities of CValueObject into separate classes will reduce the coupling between different
cross-cutting concerns and allow us to untangle the web of interdependencies and greatly simplify things.

src/blackmisc/containerbase.h

@@ -158,7 +158,7 @@ namespace BlackMisc
         }
 
         //! \copydoc BlackMisc::CValueObject::getMetaTypeId
-        virtual int getMetaTypeId() const override { return qMetaTypeId<C<T>>(); }
+        int getMetaTypeId() const { return qMetaTypeId<C<T>>(); }
 
         //! \copydoc BlackMisc::CValueObject::marshallToDbus
         virtual void marshallToDbus(QDBusArgument &argument) const override