ludus. Add object child access.

Adds another option to object child access, returns a pointer to the child.
This will be used by the game to hold pointers to specific objects in the game tree.
ludus. Add access to the ingenium audio engine.

This change also removes the audio source field from ingenium that was used for testing.
ludus. Change to game interface.

Change the on create object method. Pass the created object to the game.
The game can now set the object data directly using the passed object, so the method does not return any value.