entity system redesign

- changed system to "processing_system" to avoid conflicts
- redesigned entity systems to enable construction/destruction of
components - removed variadic functionality from entities, there are yet
still variadics when specifying systems needed components
- made a draft of entity system demo, yet to debug
- removed references to type_mapper, it's probably to be deleted
- component types are manually registered just by adding systems to the
world - all components that added systems need are automatically
registered in the component type library