Allow for component disabling for prefabs

[jtferson]

Describe the problem you are trying to solve.
Currently it's possible to disable components for regular entities. It might be useful to expand that functionality to define which components of the prefab instances will be disabled by default.

Describe the solution you'd like
Instances inherit the disabling status of components from the prefab:

// Velocity will be disabled for every instance by default
auto prefab = ecs.prefab()
	.add<Movable>()
	.add_owned<Velocity>()
	.disable<Velocity>();

// Here an instance is getting the Velocity component as disabled
auto instance = ecs.entity().add_instanceof(prefab);

// Example: a system matches only entities with enabled Velocity
ecs.system<>().signature("Velocity, Movable").iter([](flecs::iter& it)
{
       test_int(it.count(), 0);
});