Remove the `Iso * Vec` overload and the ability to Transform a Vector with an Iso.

This is too error prone as the user has to remember if he is using a vector or a point.
Istead, to transform a vector with an Isometry, use the internal rotation matrix of the isometry:
`iso.rotation * vector` instead of `iso * vector`.

The `Rotation` trait can also be used.
Do not implement `Transform<Vec*> for Vec*`.

This is error prone as this is a no-op for vectors and a translation for points.