Add more straightforward ray-cast methods to the CollisionWorld

We should add methods like the ones from the `RayCast` [trait](https://www.ncollide.org/rustdoc/ncollide3d/query/trait.RayCast.html) to the `CollisionWorld` so that it is easy to retrieve the closest object intersecting with a given ray.

In addition to their original output as defined in the `RayCast` trait, those methods would return the handle of the intersected collision object.