Use jet&met calculators from standalone package

I copied them to a separate repository&package a while ago, and now there are some other users, so I'm moving that to https://gitlab.cern.ch/cp3-cms/CMSJMECalculators , and removing here to avoid duplication of efforts / diverging code. The tests seem happy, one open question is if test_jmesystcalc.py should be removed here (or reduced)... they're fast, but the same tests.

Based on the master branch to allow for more testing, but I think the easiest is to merge after !195 (merged) and !203 (merged) are in (there will some code style fixes, but they should be minimal - other than removing lots of code this is not a big set of changes).