reduced complexity of the entity class.
entities are now only a handle wich can be resolved to the respective components in the systems.
this means handles (ids) are no longer granted per component but per entity.
with the old aproach it was hardly possible to detremine wich component belongs to wich entity.
now components have an owner. i do not remember why this was necessary. maybe in the old aproach it was useful
to get other components, stored in other system from the same entity. but now with the handles granted per entity this
advantage is obsolet.
the new aproach is acompanied by a new problem. when an entity is destroyed its components stay in the system.
without a list of typeless handles to the components or a list of component types the entity owns, its difficult
to delete all the components of the entity when it is destroyed.
NOTE: maybe the new owner pointer in the component class could be useful to solve this problem. thats why it stays
in the new revision.