DataFormats/Candidate: make CMS_CLASS_VERSION(11) public, not protected

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #2971 from davidlt/DataFormats-Candidate-make-CMS_CLASS_VERSION-public

DataFormats/Candidate: make CMS_CLASS_VERSION(11) public, not protected