New MVA taggers backport from 71X to 70X

Contains backport of the following 71X merged pull requests:
https://github.com/cms-sw/cmssw/pull/2622
https://github.com/cms-sw/cmssw/pull/3384
https://github.com/cms-sw/cmssw/pull/3664
https://github.com/cms-sw/cmssw/pull/3733

But also the unmerged 70X pull request to avoid clashes with backported code:
https://github.com/cms-sw/cmssw/pull/3394