Jvf static

Make several functions static again, after adding the JVF code.

These changes try to reduce the dependence we have on SusyNtTools.
In the long term, it will simplify the inheritance scheme we currently have,
and delegate tasks to smaller, self-contained classes.

Verified that the cutflow with Susy2LepCF does not change, but there's
one detail (see below) to be sorted out.

imported from gerbaudo/SusyNtuple_take1/pull/1