Contact information should be provided in local-space.

Currently, the [Contact](https://github.com/sebcrozet/ncollide/blob/master/ncollide_geometry/query/contacts_internal/contact.rs#L7-L20) structure contains contact information in world-space. This makes implementation of, e.g., contact tracking, more difficult. In addition, word-space information are less accurate numerically than local-space one as they depend on the world origin.