Secondary vertex clustering + explicit jet-track association

This PR adds the SV clustering capability to the SVTagInfo producer and adds the explicit jet-track association to the candidate-based IPTagInfo producer.

All changes completely transparent to the standard reconstruction.

**Update:** Rebased to CMSSW_7_3_X_2014-11-15-0200 and added support for SV clustering, jet flavor for subjets, and explicit jet-track association in PAT
Added protection for division by zero with included `edm::LogWarning`.