Switch on BTag from candidates in reco and provide corresponding PAT tools

This PR runs one candidate based tagging (exploiting the new fwk) in RECO.
The corresponding code in jetTools.py (and related PAT stuff) is also added.

@ferencek @pvmulder
We are working in parallel on another PR where I am modifying this file. If you agree can include this minor change in the next PR (it is just cosmetics anyway).