ludus. Next step to moving the tree to using node.

Add an entity constructor that can be used inisde a node impl.
Change entity constructor and destructor access to public.
Add a move constructor to object.
Add a move constructor to matrix4.
Both constructor are used in the new entity constructor.
Add a node field to entity.
ludus. Add node entity convenience type.

Fix several compile issues in node impl.
Add node entity type in entity header.