Extend traits to include VectorSpace tests and wrapped access to pTraits static members

In several places need to check pTraits<Type>::nComponents and/or pTraits<Type>::rank (eg, to decide if transforms are required).
This works well until confronted with an arbitrary type for which no pTraits exists and which doesn't have its own corresponding static members.

Use SFINAE templating to provide new trait tests:

• pTraits_rank
• pTraits_nComponents
• pTraits_has_zero
• is_vectorspace