Added label(int k) method.  This made it convenient to also make read() a template function.  Added label data buffer.
Added label(int k) method.  This made it convenient to also make read() a template function.  Added label data buffer.

git-svn-id: 602a26e73ae9f2a14e2bb95676f2e137fcc39919@3472 7c0444ca-5550-0410-9008-faecdbe78eb5

PetaVision/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,PetaVision/OpenPV,PetaVision/OpenPV,PetaVision/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,dpaiton/OpenPV,PetaVision/OpenPV,dpaiton/OpenPV