Added a BaseComponentType to VecTraits that recursively finds the base
(non-Vec) type of a Vec. This is useful when dealing with potentially
nested Vec's (e.g. Vec<Vec<T, M>, N>) and you need to keep the structure
but know the base type.

Also added a couple of templates for keeping the structure but changing
the type. These are ReplaceComponentType and ReplaceBaseComponentType.
These allow you to create new Vec's with the same structure as the query
Vec but with differen component types.