MaterialStdVectorAux added.  Fixes #3590

This allows extraction of a component of a std::vector<Real>
from a Material.
Merge pull request #3841 from WilkAndy/stdvectoraux_3590

MaterialStdVectorAux added.  Fixes #3590
Merge commit 'd4645c6349eb29b69af98398724f1c281c5864fa'