183 Calling generated methods in a Mapper via the Decorator

1. Suppose you have a tree structure of objects which are mapped by one mapper (you can of course break-up, but that should not be needed de-facto).

2. Suppose that you need to decorate a leaf deep down in this tree structure.

Currently you need to decorate each branch leading towards the leaf to be able to 'reach' it. A simple test has been added to demonstrate. This conflicts very much with the idea of making things simple. You should only decorate the methods that are strictly needed to be decorated.

I needed to create a call back in the constructor of the `DecoratorImpl`.  That should be scrutinized for better solutions.